Effects of Initial Graft Tension and Patient Sex on Knee Osteoarthritis Outcomes After ACL Reconstruction: A Randomized Controlled Clinical Trial With 10- to 12-Year Follow-up

Abstract

Background:

The initial graft tension applied during anterior cruciate ligament (ACL) graft fixation may promote posttraumatic osteoarthritis (PTOA).

Purpose/Hypothesis:

This study sought to assess the effect of initial graft tension and patient sex on PTOA outcomes at 10 to 12 years after ACL reconstruction (ACLR). The hypothesis was that there would be no group- or sex-based differences in outcomes.

Study Design:

Randomized controlled trial; Level of evidence, 1.

Methods:

Patients were randomized to receive ACLR with a low or high initial graft tension. Outcomes were evaluated at 10 to 12 years postoperatively and compared with a matched, uninjured control group. Outcomes included clinical assessments (anteroposterior [AP] knee laxity measurement, International Knee Documentation Committee [IKDC] examination score), a functional assessment (single-leg hop for distance), patient-reported outcomes (Knee injury and Osteoarthritis Outcome Score [KOOS], 36-Item Short Form Health Survey, Tegner activity level, patient satisfaction), and PTOA imaging (Osteoarthritis Research Society International [OARSI] radiographic score and Whole-Organ Magnetic Resonance Imaging Score [WORMS]). Two-way mixed-model analyses of variance were used to evaluate differences in outcomes between tension groups and the control group and between female and male patients.

Results:

Both tension groups scored worse than the control group for the IKDC examination (P≤ .021), KOOS (Pain, Activities of Daily Living, Sport/Recreation, and Quality of Life subscales) (P≤ .049), and WORMS difference score (P≤ .042). The low-tension group scored worse than the control group for KOOS Symptoms (P = .016) and the OARSI difference score (P = .015). The index limb had worse scores than the contralateral limb within the high-tension group for AP laxity (P = .030) and hop deficit (P = .011). This result was also observed within both tension groups for the WORMS (P≤ .050) and within the low-tension group for the OARSI score (P = .001). Male patients had higher Tegner scores (mean ± SE) relative to female patients (male, 5.49 ± 1.88; female, 4.45 ± 1.65) and worse OARSI difference scores (male, 1.89 ± 5.38; female, 0.244 ± 0.668) (P = .007 and .034, respectively). However, no significant differences were detected between tension groups for any of the outcomes measured.

Conclusion:

Overall, ACLR failed to prevent PTOA regardless of initial graft tension. However, male patients treated with a low initial graft tension may be at greater risk for PTOA. These results do not support the hypothesis of no sex differences in outcomes at 10 to 12 years after ACLR.

Keywords

tension sex anterior cruciate ligament (ACL)reconstruction outcomes osteoarthritis

Anterior cruciate ligament (ACL) injuries affect approximately 400,000 individuals annually in the United States³⁶ and place patients at risk for posttraumatic osteoarthritis (PTOA).³ ACL reconstruction (ACLR) is commonly performed to restore knee function and decrease the risk of PTOA after ACL injury.²¹ However, clinical studies demonstrate that PTOA often progresses despite surgical intervention.^14,19,21,33 The reason for this progression remains unclear, although the initial graft tension applied at the time of fixation has been implicated as an important contributing factor.¹⁹

Initial graft tension alters native joint contact mechanics and kinematics, which may predispose the knee to PTOA development after ACLR.¹⁰ Recommendations for graft tensioning protocols have been made, but the optimal tension to restore native knee stability, while at the same time minimizing the risk of PTOA, remains unknown. In addition, female sex is an established risk factor for ACL injury and has been suggested as a risk factor for worse outcomes after ACLR, although this remains a topic of debate, with some studies reporting worse postoperative outcomes in female patients^{1,2,9,26,29,31} and others reporting no sex-based differences.^{7,17,25,38,40,44} Short-term (ie, 3-year)¹⁸ and midterm (ie, 7-year)⁴ analyses from an ongoing randomized controlled trial examining the outcomes of 2 different initial graft tension conditions have been previously published. Minimal differences in outcome between the 2 tension cohorts at 3 and 7 years postoperatively were observed, as well as inferior clinical, functional, patient-reported, and imaging outcomes among the ACLR group relative to the matched, uninjured control participants.^4,18 No analysis of the effect of patient sex was conducted within this cohort. Because PTOA is a progressive disease, and given the emerging differences between the tension groups at the midterm time point, we sought to investigate long-term PTOA development and potential sex-based differences in outcomes among this patient cohort.

The primary aim of this longitudinal trial was to evaluate the progression of PTOA after surgical reconstruction of the ACL between low- and high-tension groups 10 to 12 years after surgery. The secondary aim was to determine how patient sex, initial graft tension, and the interaction between these variables may influence long-term clinical outcomes (anteroposterior [AP] knee laxity, International Knee Documentation Committee [IKDC] examination score), a functional outcome (single-leg hop for distance), patient-reported outcomes (Knee injury and Osteoarthritis Outcome Score [KOOS], 36-Item Short Form Health Survey [SF-36], Tegner activity level, patient satisfaction), and imaging outcomes (Osteoarthritis Research Society International [OARSI] radiographic score, Whole-Organ Magnetic Resonance Imaging Score [WORMS]) related to osteoarthritis. To our knowledge, investigation of the potential interaction between initial graft tension and patient sex in the context of long-term outcomes is a novel pursuit. The present analysis leverages the ACLR and matched, uninjured control patient cohorts from the ongoing trial evaluating the effects of initial graft tension.^4,18 We hypothesized that there would be no differences in outcomes between the 2 initial graft tension groups or between female and male patients at 10 to 12 years after ACLR.

Methods

Trial Design

The current long-term analysis is an extension of previous short-term (ie, 3-year)¹⁸ and midterm (ie, 7-year)⁴ analyses from an ongoing randomized controlled trial (NCT00434837) and leverages the follow-up data obtained at 10 and 12 years after ACLR (Figure 1). Due to the higher rate of loss to follow-up at the 12-year time point, 10-year data were substituted for missing 12-year data when available. The institutional review board of Rhode Island Hospital approved this study, and all participants provided written informed consent.

The study was designed as a randomized, double-blind, controlled trial. The randomization assignment, which was performed by the study statistician (G.J.B.), was disclosed to the operating surgeon at the time of intraoperative graft placement. All subsequent evaluations were performed by blinded assessors. Power calculations specific to analyses of long-term outcomes (ie, 10- to 12-year outcomes) were performed a priori based on available 7-year data and estimated that a sample size of 30 participants per surgical group would have sufficient power (1 –β = 0.80 using α = .05) to detect a mean difference between groups of 1.4 mm for AP knee laxity, 11.5 points (ie, less than a mild deficit⁴¹) for KOOS quality of life (QOL) subscale, and 0.50 points for the IKDC clinical examination score. For the secondary aim of evaluating sex differences, the detectable mean difference between female and male patients corresponding to 80% power was estimated to be 2% larger than those specified above. This calculation assumed a female to male ratio of 3:2 based on the 7-year data. Post hoc power calculations for other outcomes resulted in an estimated power of 80% for detecting mean differences between groups of 2.6 points for the OARSI radiographic difference score, 15.1 points for the WORMS difference score, 9.5% for the single-leg hop test ratio, and 9.8 points for the SF-36 physical functioning subscale.

Participants and Entry Criteria

All patients who had an isolated unilateral ACL injury in the clinics of 3 surgeons (P.D.F., M.J.H., R.M.S.) over 3 years (between February 2004 and February 2007) were evaluated for eligibility, as previously described.^4,18 In brief, the study included female and male patients between 15 and 50 years of age with a unilateral ACL injury who were candidates for surgical reconstruction with a bone–patellar tendon–bone (BPTB) graft or a 4-strand semitendinosus and gracilis (4-ST/G) autograft. Excluded from participation were patients >12 months out from their date of ACL injury; patients who had meniscal tears requiring partial meniscectomy involving more than one-third of the meniscus; patients with increased clinical laxity of the medial collateral ligament, lateral collateral ligament, or posterior cruciate ligament; patients who had a previous knee injury; and patients with radiographic evidence of degenerative arthritis. Of the 557 patients screened, 355 were excluded and 112 declined to participate.^4,18 An uninjured control group was also recruited from the local area via advertisement.^4,18 This group consisted of 60 participants who were matched to the participants with ACLR by age (ie, 18-50 years), sex, race (ie, African American, Hispanic, White, other), and activity level (ie, Tegner score ≥2). Control participants were excluded if they had a previous knee injury; if they had increased clinical knee laxity of the medial collateral ligament, lateral collateral ligament, or posterior cruciate ligament relative to the control knee; or if they had evidence of degenerative arthritis on radiographic assessment.

Protocols for ACLR and Initial Graft Tension

ACLs were reconstructed using either a BPTB autograft obtained from the central third of the ipsilateral patellar tendon or a 4-ST/G autograft.^4,18 Participants chose the graft type in consultation with their surgeon, and all surgeons adhered to the same operative procedures, which entailed use of the transtibial technique for femoral tunnel drilling. Grafts were preconditioned with 20 manual tension cycles before fixation. Bone blocks for the BPTB autografts were secured using interference screws (Titanium Interference screws, 7 × 20, 8 × 20, and 9 × 20; Arthrex), and the 4-ST/G autografts were fixed with cortical fixation on the femur (Endobutton; Smith & Nephew) and a biodegradable interference screw on the tibia (Biointrafix, small or large sheath with 8- or 9-mm tapered screw; DePuy Mitek), reinforced at the surgeon’s discretion using a screw and spiked soft tissue washer (Acufex Spiked Washer/Tibial Anchor; Smith & Nephew). Grafts were tensioned following a “laxity-based” approach, where the level of graft tension (ie, low vs high) was determined indirectly based on the AP laxity value of the index knee relative to the contralateral knee at the time of fixation. Grafts for the low-tension assignment were tensioned with the knee at 0° of flexion such that the AP laxity of the index knee matched that of the contralateral knee,^4,18 and grafts for the high-tension assignment were tensioned with the knee at 30° of flexion such that the AP laxity value of the index knee was overconstrained by 2 mm relative to the contralateral knee.^4,18 The rationale behind this laxity-based approach is that the level of tension applied to recreate normal AP knee laxity would be less than that required to overconstrain the joint within the same patient if the tensioning was performed at the same knee flexion angle. The knee flexion angles used in this protocol contributed to establishing the distinct graft tension conditions because overconstraining AP laxity by firmly tensioning the graft with the knee at 30° of flexion (ie, the high-tension assignment), the knee angle where the ACL is under less tension, would result in heightened graft tension across all angles of the extension-flexion cycle compared with the low-tension group in which the graft was tensioned in full extension (0°), where the ACL is at the greatest tension. Tibial fixation was partially engaged for both graft types, and AP laxity at 20° of flexion was evaluated using a sterilizable knee arthrometer (KT-1000S; MEDmetric Corp) and compared with that of the contralateral knee under anesthesia. If the targeted knee laxity value was not achieved within 1 mm, fixation was released, and the tensioning procedure was repeated. The laxity value was verified when the fixation procedure was complete. Postoperatively, all participants followed a standardized rehabilitation program designed for return to sports at 6 months.⁸

Clinical Outcomes

AP laxity was measured for both knees using a knee arthrometer (KT-1000; MEDmetric Corp) for clinical assessment.¹⁵ A total of 3 manual maximum tests were performed, and the displacement readings were averaged. The difference between knees (index minus contralateral) was calculated, compared, and reported.

Clinical outcomes were assessed using the IKDC 2000 examination score.²⁴ This score rates knees as normal (A), nearly normal (B), abnormal (C), or severely abnormal (D) based on knee function, symptoms, and range of motion, with the final IKDC examination rating based on the worst overall score. A trained sports physical therapist (S.L.F.) administered all clinical examinations.

Functional Outcomes

Participants performed the single-leg hop test for distance 3 times per leg for functional assessment, and the trials within each leg were averaged.¹¹ A mean hop deficit value was calculated as the quotient of the average index limb hop values and average contralateral limb hop values multiplied by 100.

Patient-Reported Outcomes

The KOOS⁴¹ and SF-36⁵¹ questionnaires were used to collect patient-reported outcomes. The KOOS evaluates 5 domains: (1) KOOS Quality of Life (QOL), (2) KOOS Sport and Recreation (Sport), (3) KOOS Activities of Daily Living (ADL), (4) KOOS Symptoms, and (5) KOOS Pain. In addition, the composite KOOS model developed by Englund et al¹⁶ was used to identify patients with symptomatic osteoarthritis. Patients with a KOOS QOL value ≤87.5 and with ≥2 of the other subscales meeting the model criteria (ie, KOOS Pain ≤86.1, KOOS Symptoms ≤85.7, KOOS ADL ≤86.8, and KOOS Sport ≤85.0) were designated as having symptomatic osteoarthritis.^16,52 The SF-36 evaluates health status related to physical functioning, physical role limitations, bodily pain, vitality, social functioning, emotional role, mental health, and general health.⁵¹

Physical activity levels were monitored using the Tegner activity scale, which grades activity level based on work and sports activity on a scale of 0 to 10, where 0 represents physical disability due to knee problems and 10 represents national- or international-level soccer participation.⁴⁸ In addition, we administered a supplemental survey where participants were asked whether they had any subsequent knee injuries that required a doctor’s visit, how satisfied they were with their surgical outcome (1 = not satisfied, 10 = very satisfied), and whether they would elect to undergo ACLR surgery again.

Osteoarthritis Imaging Outcomes

Radiographic Scoring

The overall condition of the knee joint was evaluated using the modified OARSI radiographic score.⁵ Posteroanterior and lateral radiographs of both knees were graded on a scale of 0 (normal) to 4 (severe) based on osteophyte formation and joint space narrowing. Sclerosis, attrition, and ligament calcification were assessed on a dichotomous scale. An experienced musculoskeletal radiologist (H.C.G.) scored all radiographs while blinded to group assignment.

Magnetic Resonance Imaging Scoring

PTOA was assessed via magnetic resonance imaging (MRI) using the WORMS.³⁹ This scoring system uses magnetic resonance sequences to grade 14 independent features in 15 joint regions.³⁹ These features include cartilage signal and morphology, subarticular bone marrow abnormalities, subarticular cysts, subarticular bone attrition, and marginal osteophytes. The conditions of the menisci and cruciate and collateral ligaments, as well as the presence of loose bodies and periarticular cysts, were also assessed as part of this score. The WORMS evaluations were performed by an experienced musculoskeletal radiologist (H.C.G.) who was blinded to group assignment. Details pertaining to the MRI sequences used for WORMS analysis are included in Table 1.

Table 1

MRI Sequences and Acquisition Parameters for WORMS Analysis^a

MRI Sequence	Acquisition Parameters
Sagittal T1-weighted WE 3D FLASH	TR/TE, 20 ms/7.6 ms Flip angle, 12° FOV, 160 mm Slice thickness/interslice gap, 1.5 mm/0 mm 80 slices per slab BW, 130 Hz/pixel Matrix, 512 × 512 Phase encoding axis, right/left 1 average of 2 excitations
Coronal intermediate-weighted TSE	TR/TE, 3850 ms/29 ms ETL, 7 FOV, 140 mm Slice thickness/interslice gap, 3 mm/0 mm 41 slices per slab BW, 352 Hz/pixel Matrix, 307 × 384 Phase encoding axis, anterior/posterior 1 average of 2 excitations
Sagittal T2*-weighted WE 3D DESS	TR/TE, 16.3 ms/4.7 ms Flip angle, 25° FOV, 140 mm Slice thickness/interslice gap, 0.7 mm/0 mm BW, 185 Hz/pixel Matrix, 307 × 384 Phase encoding axis, anterior/posterior 1 average of 2 excitations
Sagittal intermediate-weighted TSE with fat-saturation	TR/TE, 3460 ms/36 ms ETL, 5 FOV, 160 mm Slice thickness/interslice gap, 3 mm/0 mm BW, 248 Hz/pixel Matrix, 314 × 448 Phase encoding axis, superior/inferior 1 average of 2 excitations

3D, 3-dimensional; BW, bandwidth; DESS, double-echo steady state; ETL, echo train length; FLASH, fast low-angle shot; FOV, field of view; MRI, magnetic resonance imaging; TE, echo time; TR, repetition time; TSE, turbo spin-echo; WE, water excitation; WORMS, Whole-Organ Magnetic Resonance Imaging Score.

Statistical Analysis

Two-way mixed-model analyses of variance were used to evaluate sex and group differences in long-term (10- to 12-year) continuous outcome measures. The statistical models included fixed factors representing sex (female, male), group (low tension, high tension, and control), and their interaction. If significant interactions were detected, F tests corresponding to simple effects (ie, group sex effects within group or group effects within sex) were examined. Pairwise comparisons among group means were performed using the Fisher least significant difference procedure. Linear contrasts were constructed to test for sex differences limiting comparisons to participants in the 2 surgical groups (ie, excluding control participants). For those outcome measures reported as a difference score between index and contralateral knees (ie, AP laxity, OARSI, WORMS) or as a ratio (ie, single-leg hop test), the left or right knee was randomly chosen in control participants to represent the index limb. For limb-specific outcomes, paired t tests were used to compare index with contralateral limbs within groups. All means presented for continuous outcomes are least squares means (95% CIs).

Chi-square tests were used to evaluate sex and group effects on IKDC examination scores, the frequency of subsequent injuries, and the percentage of patients in whom the composite KOOS model⁵² indicated the presence of symptomatic osteoarthritis. Statistical significance was evaluated based on P < .05. All analyses were performed using SAS statistical software (SAS Institute, version 9.4).

Results

Participant Characteristics

At 10 to 12 years after ACLR, 32 participants in the low-tension group (18 female and 14 male), 28 participants in the high-tension group (16 female and 12 male), and 35 participants in the control group (15 female and 20 male) were available for follow-up (Figure 1). We found no significant difference between groups in the rate of loss to follow-up among the available participants (31%, 36%, and 42% for the low-tension, high-tension, and control groups, respectively; P = .492). Additional details are provided in Appendix Table A1 (available in the online version of this article). Age, body weight, number of days from injury to surgery, patient sex, ethnicity, and graft type were not significantly different between groups (Table 2).

Table 2

Characteristics of Participants Included in the 10- to 12-Year Follow-up^a

Characteristics	Low Tension (n = 32)	High Tension (n = 28)	Control (n = 35)	P Value
Age, y, mean ± SD	24.8 ± 9.3	22.3 ± 6.9	26.2 ± 7.1	.143
Weight, kg, mean ± SD	74.0 ± 14.9	69.8 ± 16.7	69.7 ± 12.0	.396
Days to surgery, median [IQR]	90 [62.5-162.5]	99 [56-164]	—	.982
Patient sex				.429
Female	18 (56.3)	16 (57.1)	15 (42.9)	—
Male	14 (43.8)	12 (42.9)	20 (57.1)	—
Ethnicity				.502
White, non-Hispanic	31 (96.9)	25 (89.3)	32 (91.4)	—
Other	1 (3.1)	3 (10.7)	3 (8.6)	—
Graft type				.496
BPTB	19 (59.4)	19 (67.9)	—	—
4-ST/G	13 (40.6)	9 (32.1)	—	—

Data are expressed as n (%) unless otherwise noted. 4-ST/G, 4 strand hamstrings tendon graft; BPTB, bone–patellar tendon–bone graft; IQR, interquartile range. Dashes indicate not applicable.

Clinical Outcomes

The distribution of IKDC examination scores was significantly different across groups (Table 3), with both the low- and high-tension groups scoring significantly worse than the control group (P < .001 and P = .021, respectively). No significant difference was observed between the low- and high-tension groups (P = .063), and we found no evidence of a difference in the distribution of IKDC examination scores between female and male patients. A detailed presentation of the IKDC examination results is provided in Appendix Tables A2 through A13 (available online).

Table 3

IKDC Examination Outcomes Overall and Among Female and Male Patients at 10 to 12 Years After Anterior Cruciate Ligament Reconstruction^a

	Overall			Female Patients			Male Patients			P Values
IKDC Examination Score	Low Tension^b (n = 27)	High Tension^b (n = 22)	Control (n = 27)	Low Tension (n = 15)	High Tension (n = 13)	Control (n = 11)	Low Tension (n = 12)	High Tension (n = 9)	Control (n = 16)	Group	Sex	Inter- action
A (normal)	7 (25.9)	9 (40.9)	22 (81.5)	4 (26.7)	6 (46.2)	9 (81.8)	3 (25.0)	3 (33.3)	13 (81.3)	<.001	.726	—
B (nearly normal)	19 (70.4)	8 (36.4)	4 (14.8)	10 (66.7)	4 (30.8)	1 (9.1)	9 (75.0)	4 (44.4)	3 (18.8)
C (abnormal)	1 (3.7)	3 (13.6)	00 (0.0)	1 (6.7)	2 (15.4)	00 (0.0)	00 (0.0)	1 (11.1)	00 (0.0)
D (severely abnormal)	00 (0.0)	2 (9.1)	1 (3.7)	00 (0.0)	1 (7.7)	1 (9.1)	00 (0.0)	1 (11.1)	00 (0.0)

Values are expressed as n (%). IKDC, International Knee Documentation Committee.

Values are significantly different from those of the control group. Dash indicates not applicable.

We found no significant group or sex differences in AP laxity as measured using the knee arthrometer and no evidence of interaction between these factors (Table 4). However, AP laxity was significantly worse in the index knee compared with the contralateral knee within the high-tension group (P = .030). No significant differences were detected in AP laxity between the low- and high-tension groups (P = .611). Additional information is available in Appendix Table A14 (available online).

Table 4

Knee Arthrometer AP Laxity and Single-Leg Hop Deficit Outcomes at 10 to 12 Years After Anterior Cruciate Ligament Reconstruction^a

Outcomes	Overall			Female Patients			Male Patients			P Values
Outcomes	Low Tension	High Tension	Control	Low Tension	High Tension	Control	Low Tension	High Tension	Control	Group	Sex	Interaction
AP laxity	1.2 [−0.2 to 2.7] (n = 27)	1.8^b[0.2 to 3.4] (n = 22)	0.1 [−1.4 to 1.5] (n = 27)	1.6 [−0.3 to 3.5] (n = 15)	2.1 [0.1 to 4.2] (n = 13)	−0.2 [−2.4 to 2.0] (n = 11)	1.0 [−1.2 to 3.0] (n = 12)	1.5 [−1.0 to 3.9] (n = 9)	0.3 [−1.5 to 2.2] (n = 16)	.265	.761	.803
Hop deficit	96 [91 to 102] (n = 25)	93^b [87 to 98] (n = 22)	99 [94 to 104] (n = 26)	94 [87 to 100] (n = 15)	92 [85 to 99] (n = 13)	97 [89 to 105] (n = 10)	99 [91 to 107] (n = 10)	94 [85 to 102] (n = 9)	100 [94 to 107] (n = 16)	.290	.272	.919

Values are expressed as mean [95% CI]. Anteroposterior (AP) laxity was calculated as Index Leg – Contralateral Leg and expressed in mm. Single-leg hop deficit was calculated as (Index Leg ÷ Contralateral Leg) × 100.

Values are significantly different between index and contralateral knees.

Functional Outcomes

We noted no significant sex or group differences in hop deficit and no evidence of interaction between these factors (Table 4). Additionally, no differences in hop distance were detected between the low- and high-tension groups (P = .331). However, significant differences in hop distance were observed between the index and contralateral knees within the high-tension group (P = .011). Additional details are available in Appendix Table A15 (available online).

Patient-Reported Outcomes

Group differences were significant for all 5 KOOS subscales (Table 5). KOOS subscale differences (mean ± SE) for control versus low- and high-tension groups, respectively, were as follows: KOOS Symptoms, 9 ± 3 and 7 ± 3; KOOS Pain, 6 ± 2 and 6 ± 3; KOOS ADL, 3 ± 2 and 5 ± 2; KOOS Sport, 9 ± 3 and 8 ± 4; KOOS QOL, 9 ± 4 and 16 ± 5. The low-tension group scored significantly worse than the control group for KOOS Symptoms (P = .016), and the low- and high-tension groups both scored significantly worse than the control group for KOOS Pain (P = .008 and P = .013, respectively), KOOS Sport (P = .018 and P = .037, respectively), KOOS QOL (P = .045 and P < .001, respectively), and KOOS ADL (P = .049 and P = .008, respectively). No significant differences were observed between the low- and high-tension groups for any of the KOOS subscales (P≥.101). In addition, we found no significant difference between female and male patients or evidence of any group by sex interaction for these outcomes (Table 5).

Table 5

Patient-Reported Outcomes (KOOS, Tegner, Patient Satisfaction) at 10 to 12 Years After Anterior Cruciate Ligament Reconstruction^a

	Overall			Female Patients			Male Patients			P Values
Patient-Reported Outcome	Low Tension(n = 32)	High Tension(n = 27)	Control(n = 35)	Low Tension(n = 18)	High Tension(n = 15)	Control(n = 15)	Low Tension(n = 14)	High Tension(n = 12)	Control(n = 20)	Group	Sex	Inter- action
KOOS Symptoms	83^b[79-88]	85[80-90]	92[87-96]	85[78-91]	86[79-93]	90[83-97]	82[75-89]	84[76-92]	93[87-99]	.038	.881	.670
KOOS Pain	91^b[87-94]	91^b[87-95]	97[94-101]	92[88-97]	93[88-98]	98[93-103]	89[84-94]	89[83-95]	97[93-102]	.011	.243	.771
KOOS ADL	96^b[93-98]	94^b[91-97]	99[97-102]	97[94-101]	96[92-100]	99[95-103]	94[90-98]	92[88-97]	100[96-103]	.022	.181	.570
KOOS Sport	85^b[80-90]	86^b[80-91]	94[89-98]	88[82-95]	85[78-93]	91[84-98]	82[75-90]	86[78-94]	96[90-102]	.033	.993	.302
KOOS QOL	85^b[79-92]	78^b[71-84]	94[88-100]	85[77-94]	78[70-87]	93[84-102]	85[76-94]	77[67-87]	95[88-103]	.002	.928	.915
Tegner score	4.6^c[4.0-5.2]	5.3[4.6-5.9]	5.1[4.5-5.7]	3.8[3.0-4.6]	4.9[4.1-5.8]	4.7[3.8-5.6]	5.4[4.5-6.4]	5.6[4.6-6.6]	5.5[4.7-6.2]	.375	.007	.526
Satisfaction	8.9[8.3-9.4]	9.0[8.4-9.6]	—	8.9[8.1-9.6]	9.2[8.4-10]	—	8.9[8.0-9.7]	8.8[7.8-9.7]	—	.821	.580	.633

Values are expressed as mean [95% CI]. Satisfaction was scored on a scale of 1 to 10. The KOOS Symptoms, Tegner score, and satisfaction outcomes had 1 additional female patient in the high-tension group, resulting in an overall sample size of 28 for that group. These differences in sample size are not indicated in the table. ADL, Activities of Daily Living; KOOS, Knee injury and Osteoarthritis Outcome Score; QOL, knee-related Quality of Life; Sport, Sport and Recreation. Dashes indicate not applicable.

Values are significantly different from those of the control group.

Values are significantly different between female and male patients.

Based on the composite KOOS model, 10 patients in the low-tension group (31.3%), 7 patients in the high-tension group (25.9%), and 3 patients in the control group (8.6%) had scores indicative of symptomatic osteoarthritis. Overall, no sex or group differences were observed (P = .368 and P = .060, respectively), and no significant differences were detected between the low- and high-tension groups (P = .653). However, when this analysis was performed between the combined tension groups and control group, the group difference was significant (P = .020) (Appendix Tables A16 and A17, available online).

We found no significant sex or group differences for any of the SF-36 subscales (P≥ .180 and P≥ .221, respectively) and no evidence of interaction between these factors (P≥ .249). Additionally, no significant differences were observed between the low- and high-tension groups on any of the SF-36 subscales (P≥ .214) (Appendix Table A18, available online).

No significant overall group differences were found for the Tegner activity level score (Table 5), and no significant differences were detected between the low- and high-tension groups (P = .176). However, significant differences between female and male patients were observed for this outcome (Table 5). Although we found no evidence that sex differences were group dependent (P = .523), this difference was most pronounced in the low-tension group, in which female patients scored significantly worse than male patients (P = .013). Male and female activity levels were not significantly different in either the high-tension group or control group (P = .341 and P = .198, respectively).

We found no significant sex or group differences between low- and high-tension groups (P = .821) for the satisfaction outcome and no evidence of interaction between these factors. Satisfaction was generally high, averaging approximately 9 on a 10-point scale among patients in the surgical tension groups (Table 5).

A total of 28 participants included in the 10- and 12-year follow-up reported a total of 39 subsequent injuries since their initial baseline visit. Of these injuries, 5 were ACL graft failures, and 8 were contralateral ACL tears. Of the ACL graft failures, 3 occurred in the high-tension group, and 2 occurred in the low-tension group. Of the contralateral ACL tears, 3 occurred in the low-tension group, 4 occurred in the high-tension group, and 1 occurred in the control group. Appendix Table A19 (available online) provides a detailed history of subsequent injuries in the affected participants.

Imaging Outcomes

Significant group effects were observed for the MRI-based WORMS difference score (ie, index-contralateral) (Table 6). The low- and high-tension groups scored significantly worse than the control group (P = .002 and P = .042, respectively), although there was no significant difference between tension groups (P = .374) (Table 6). Mean WORMS values for the index knee were significantly worse than were those for the contralateral knee in both the low- and high-tension groups (P = .001 and P = .050, respectively). These knee differences were primarily due to male patients whose index knee had higher scores, indicating a worse overall knee condition, than the contralateral knee in both the low-tension (P < .001) and high-tension (P = .058) groups. WORMS difference scores were not significantly different between female and male patients when control participants were included (P = .061) but were significantly higher in male patients compared with female patients among the 2 tension groups exclusively (P = .008) (Appendix Table A20, available online). No significant interaction of sex and group was observed (Table 6).

Table 6

WORMS and OARSI Difference Score Outcomes at 10 to 12 Years After Anterior Cruciate Ligament Reconstruction^a

	Overall			Female Patients			Male Patients			P Values
Image Score	Low Tension	High Tension	Control	Low Tension	High Tension	Control	Low Tension	High Tension	Control	Group	Sex	Inter- action
WORMS	13.3^{b , c}[6.1 to 20.6](n = 26)	8.3^{b , c}[0.2 to 16.5](n = 21)	−3.4[−10.8 to 4.1](n = 25)	2.5[−6.9 to 11.9](n = 15)	4.0[−6.1 to 14.1](n = 13)	−1.1[−12.6 to 10.4](n = 10)	24.1[13.2 to 35.1](n = 11)	12.7[−0.2 to 25.6](n = 8)	−5.7[−15.1 to 3.7](n = 15)	.008	.061	.054
OARSI score	2.4^{b , c , d}[1.1 to 3.8](n = 27)	1.0[−0.6 to 2.6](n = 21)	0.0[−1.4 to 1.4](n = 26)	0.5[−1.3 to 2.3](n = 15)	0.1[−1.9 to 2.0](n = 13)	0.1[−2.0 to 2.2](n = 11)	4.4[2.4 to 6.4](n = 12	1.9[−0.5 to 4.4](n = 8)	−0.2[−2.0 to 1.6](n = 15)	.050	.034	.106

Values are expressed as mean [95% CI]. OARSI, Osteoarthritis Research Society International; WORMS, Whole-Organ Magnetic Resonance Imaging Score.

Values are significantly different from those of the control group.

Values are significantly different between index and contralateral knees.

Values are significantly different between female and male patients.

Significant group differences were observed for the radiograph-based OARSI difference score (ie, index-contralateral) (P = .050) (Table 5), with the low-tension group scoring significantly worse relative to the control group (P = .015). We observed no significant difference in this score between the high-tension and control groups (P = .341) and no significant difference between tension groups (P = .179). Additionally, the index and contralateral knees had significantly different OARSI scores within the low-tension group (P = .001), which was primarily due to the male patients within that group whose index knee scored significantly worse than the contralateral knee (P < .001). Furthermore, male patients had significantly higher OARSI difference scores than female patients had (P = .034) (Table 6). This difference was most pronounced in the low-tension group, in which male patients scored significantly worse than female patients (P = .006). The difference between female and male patients remained significant when analyses were limited to patients in the 2 tension groups exclusively (P = .008) (Appendix Table A20, available online). No interaction of sex and group was observed (Table 6).

Discussion

In this study we sought to evaluate how initial graft tension and patient sex influence PTOA outcomes at 10 to 12 years after ACLR. The results demonstrated no significant differences between the tension groups, as hypothesized. However, independent group and sex main effects were observed for the IKDC examination, KOOS, WORMS difference score, and OARSI difference score outcomes and the Tegner and OARSI difference score outcomes, respectively. The finding of patient sex-based differences did not support the hypothesis that there would be no differences in outcome between female and male patients at 10 to 12 years after ACLR.

No significant differences between the low- and high-tension groups were detected for any of the functional or clinical outcomes assessed in this study. This finding is consistent with several randomized trials that have evaluated the effects of initial graft tension on clinical outcomes after ACLR. For hamstring tendon grafts, Kim et al²⁷ found no significant differences in knee laxity when grafts were tensioned to 78, 117, and 146 N at 1 year after surgery. For BPTB grafts, Yoshiya et al⁵⁶ and van Kampen et al⁵⁰ found no differences in knee laxity based on initial graft tension after ACLR using BPTB grafts. Similarly, Chahal et al¹² recently investigated differences in postoperative outcomes based on graft fixation angle (ie, 0° vs 30° of flexion), which corresponds to low and high graft tensions in the current study, respectively, and determined no differences between groups for AP stability as well as no differences in any of the KOOS subdomains; secondarily, those investigators did find that patients who underwent graft fixation in full extension had higher Marx activity scores and were more likely to reach the minimal clinically important difference for KOOS Pain. Conversely, Nicholas et al³⁷ reported significant improvements in knee laxity when BPTB grafts were tensioned to 90 N compared with 45 N, although no differences were detected in other functional outcomes, including the Knee Outcome Survey and single-limb hop test. Evidence-based reviews by Arneja et al⁶ and Kirwan et al²⁸ summarized the discrepancies concerning the effects of initial graft tension on postoperative outcomes, finding no clear trend in terms of statistically significant or clinically relevant differences based on initial graft tension and insufficient evidence to conclude whether postoperative function is improved at any specific tension level, respectively. These findings, which align with those of the present study, call into question the clinical relevance of initial graft tension as related to postoperative outcomes and warrant future investigation.

The low- and high-tension groups scored significantly worse than the control group for the IKDC examination, KOOS (Pain, ADL, Sport, and QOL subscales), and WORMS difference score outcomes at 10 to 12 years after ACLR. Collectively, these findings suggest that ACLR failed to mitigate PTOA risk regardless of initial graft tension, which is consistent with the existing literature.^4,18,19 Interestingly, the low-tension group alone scored worse than the control group for the KOOS Symptoms and OARSI difference score outcomes, suggesting that a low initial graft tension may predispose patients to arthrosis that is not reflected by the IKDC examination, KOOS (Pain, ADL, Sport, and QOL subscales), or WORMS difference score outcomes. However, among female and male patients, the low-tension group tended to have worse IKDC examination scores relative to the control group (Appendix Tables A9 and A10, available online), suggesting that this score may have an emerging sensitivity to osteoarthritic changes within this group. In addition, the difference between the high-tension and control groups for KOOS Symptoms approached significance at this time point (P = .06) (Supplemental Table S16), suggesting that arthrosis may be progressing in this group. This point is consistent with the findings that the index knee scored worse than the contralateral knee within the high-tension group for the AP laxity and single-leg hop deficit outcomes (Appendix Tables A14 and A15), which could suggest the progression of arthrosis in the surgical knee within this group. Additional long-term follow-up is warranted to determine whether the KOOS Symptoms trend will emerge as significant at later time points.

Female patients had significantly worse Tegner scores than male patients had at 10 to 12 years after ACLR. This finding suggests that female patients maintained a lower physical activity level than male patients, which could suggest a relative functional deficit between female and male patients postoperatively. However, female sex did not emerge as a risk factor for any of the other outcomes assessed, and this result was also observed in the control group, which suggests that this finding may be related to other extrinsic factors unrelated to surgery. In contrast, male patients had significantly worse OARSI difference scores relative to female patients, suggesting that male patients have more radiographic signs of PTOA relative to female patients at this postsurgery time point. In addition, there is evidence that this result was primarily influenced by male patients within the low-tension group, suggesting that a low initial graft tension may predispose male patients to worse PTOA. Collectively, the OARSI difference score and Tegner sex-based findings may indicate that a higher level of physical activity after ACLR promotes PTOA in the affected knee, which is consistent with the results of a long-term study by Curado et al,¹³ where a moderate or strenuous level of physical activity 22 years after ACLR, specifically engagement in pivot or pivot-contact sports, was identified as a PTOA risk factor. Importantly, the OARSI sex-based result aligns with the findings that the index knee had significantly worse OARSI and WORMS difference score outcomes relative to the contralateral knee among male patients in the low-tension group, implicating the progression of osteoarthritis in the surgical knee among male patients within this group. This result is also consistent with the composite KOOS model assessment of symptomatic osteoarthritis, which demonstrated that the difference between the combined tension groups and the control group approached significance among male patients (Appendix Tables A16 and A17, available online). Furthermore, there was evidence that this difference was primarily influenced by the low-tension group, again suggesting male sex and low initial graft tension are risk factors for PTOA (Appendix Tables A16 and A17). The strong trend that male patients in the low-tension group had worse WORMS difference scores than female patients had further supports this finding. Given that we observed no significant differences between tension groups or interaction of sex and group, these findings bear further investigation.

Examination of OARSI difference and WORMS difference scores revealed osteophytes and cartilage degeneration as the primary drivers of poor imaging outcomes at the 10- to 12-year time point. Given this agreement, it is unclear why male sex emerged as a significant risk factor for worse OARSI difference scores but not for worse WORMS difference scores. Interestingly, when this analysis was performed among the tension groups exclusively, this difference became significant, suggesting that the effect of male sex on the WORMS difference scores may be dependent on initial graft tension (Appendix Table A20, available online). The clinical significance of these findings remains unclear, as male sex did not emerge as a risk factor for the other outcomes assessed at this postsurgery time point. Furthermore, the finding of male sex as a potential PTOA risk factor is largely inconsistent with the existing literature, which—albeit controversial— predominantly reports female sex as a PTOA risk factor after ACLR (or no sex-based effects at all).^26,35 However, Salmon et al⁴² reported a trend where early radiological signs of degeneration were higher in male patients relative to female patients at 7 years after ACLR. Additional long-term studies of PTOA risk among female and male patients after ACLR are therefore warranted.

Previous studies have reported female sex as a risk factor for worse KOOS (Sport,² QOL,² and Pain³⁰), knee laxity,^42,47,53 SF-36 (physical role limitations, bodily pain, and general health),¹⁷ and IKDC examination^30,53 outcomes after ACLR, whereas the present study detected no sex differences in these assessments. Although the reasons for these discrepancies remain unclear, it is important to note that the referenced studies were conducted with short- to midterm follow-up, whereas the present study was conducted with longer-term follow-up. Thus, it is possible that the reported sex differences occur at early postsurgery time points and resolve in the long term, as suggested by a study where minor sex differences were initially observed for KOOS results at 9 months postoperatively but were no longer detectable at the 12-month follow-up.⁴⁹ Furthermore, because the cohort leveraged in the present study was assessed for sex differences only at 10 to 12 years postoperatively, the time point at which these differences emerged is unknown. Future research is therefore required to investigate the emergence and duration patterns for sex differences in these postoperative outcomes.

There are several study limitations to consider. Given the loss to follow-up rate at 10 to 12 years postoperatively (36.7%), the study was sufficiently powered to detect relatively large effect sizes (Cohen d = 0.74%). As a result, smaller magnitude differences cannot be ruled out. In addition, although the radiologist was blinded to the treatment group, it is possible that the presence of screws and tunnels in the surgical knee biased scoring of the radiographs or MRI scans. However, the radiologist would not have been able to distinguish the contralateral images between the control and tension groups or initial graft tension among knees reconstructed using either autograft type. An additional limitation to consider is the use of both BPTB and 4-ST/G autografts, which was initially justified because previous studies had shown that the autograft types had similar biomechanical properties^54,55 and postoperative outcomes, and the autograft type thus was thought not to result in postoperative outcome differences.^22,23,34 However, although both graft types are deemed viable options for primary ACLR, recent meta-analyses comparing the postoperative outcomes of BPTB and 4-ST/G autograft use in ACLR demonstrated that 4-ST/G autografts may fail at a higher rate and produce inferior static knee stability relative to BPTB autografts.^20,43,45 Furthermore, ACLR using 4-ST/G autografts has been shown to produce worse outcomes in female patients relative to male patients.^32,46,42 These graft-based differences could potentially confound the findings of this study; however, the proportion of graft types in the 2 tension groups was similar and thus should have mitigated this effect (Appendix Table A1, available online). Ultimately, the potential effect of graft type on outcomes could not be assessed because graft type was self-selected (ie, not randomized) and the sample size was insufficient to address this question.

In conclusion, the study results supported the hypothesis that ACLR produced inferior outcomes relative to the matched, uninjured control group and that the procedure did not prevent the onset of PTOA in the knee-injured cohort, regardless of initial graft tension. Furthermore, no differences in outcomes were detected between the low- and high-tension groups. However, the results did not support the hypothesis that there would be no difference in outcomes between female and male patients, as sex differences were observed for the Tegner activity level and OARSI difference scores. Cumulatively, these findings suggest that male patients treated with a low initial graft tension may be at higher risk for PTOA postoperatively.

Supplemental Material

sj-pdf-1-ajs-10.1177_03635465221124917 – Supplemental material for Effects of Initial Graft Tension and Patient Sex on Knee Osteoarthritis Outcomes After ACL Reconstruction: A Randomized Controlled Clinical Trial With 10- to 12-Year Follow-up

Supplemental material, sj-pdf-1-ajs-10.1177_03635465221124917 for Effects of Initial Graft Tension and Patient Sex on Knee Osteoarthritis Outcomes After ACL Reconstruction: A Randomized Controlled Clinical Trial With 10- to 12-Year Follow-up by Meggin Q. Costa, Gary J. Badger, Cynthia A. Chrostek, Orianna D. Carvalho, Stacy L. Faiola, Paul D. Fadale, Michael J. Hulstyn, Holly C. Gil, Robert M. Shalvoy and Braden C. Fleming in The American Journal of Sports Medicine

Footnotes

Submitted June 15, 2022; accepted July 26, 2022.

One or more of the authors has declared the following potential conflict of interest or source of funding: This study was funded by support from the National Institutes of Health (NIAMS R01-AR047910 and NIAMS R01-AR074973) and the Lucy Lippitt Endowment. M.J.H. has received travel expenses from Arthrex Inc. R.M.S. has received consulting fees from DePuy Synthes Products and Medical Device Business Services and travel expenses from Stryker Corporation. B.C.F. is a cofounder of Miach Orthopaedics; his spouse has an equity interest in the company. B.C.F. serves as an associate editor for the American Journal of Sports Medicine, receives royalties from Springer Publishing, has received educational travel support from Smith & Nephew, and has received consulting fees from New York R&D Center for Translational Medicine and Therapeutics, Inc. B.C.F. maintains a conflict-of-interest management plan that is managed by Rhode Island Hospital. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

ORCID iD

Braden C. Fleming

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