Anatomic Features of the Tibial Plateau Predict Outcomes of ACL Reconstruction Within 7 Years After Surgery

Abstract

Background:

Multiple anatomic features of the femoral condyles and tibial plateau have been shown to influence knee biomechanics and risk of anterior cruciate ligament (ACL) injury. However, it remains unclear how these anatomic factors affect the midterm outcomes of ACL reconstruction.

Hypothesis:

Decreased femoral notch width, increased posterior and coronal slopes, and decreased concavity of the tibial plateau are associated with inferior clinical, patient-reported, and osteoarthritis-related outcomes 7 years after ACL reconstruction.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

Prospectively collected data from 44 patients who did not have a subsequent graft or contralateral ACL failure within 7 years after unilateral ACL reconstruction were reviewed (mean ± SD age, 23.7 ± 9.2 years; 64% women). Notch width (after notchplasty), posterior slopes of the medial and lateral tibial plateau, maximum depth of the medial tibial plateau, and coronal tibial slope were measured from magnetic resonance images. Anatomic predictors of side-to-side differences in anterior-posterior knee laxity, Knee injury and Osteoarthritis Outcome Score (KOOS), medial joint space width, and side-to-side differences in Osteoarthritis Research Society International (OARSI) x-ray score, measured at 7 years, were identified with linear regression (bivariate) and stepwise regression (multivariate).

Results:

Increased posterior slope of the lateral tibial plateau was associated with increased side-to-side difference in knee laxity (bivariate model only), increased side-to-side difference in the OARSI score, and decreased KOOS subscores (R² > .10, P < .05). Increased posterior slope of the medial tibial plateau was associated with a higher side-to-side difference in the OARSI x-ray score (bivariate model only) and lower KOOS subscores (R² > .11, P < .03). Increased coronal tibial slope was associated with lower KOOS subscores (R² > .11, P < .03). Decreased medial tibial depth was associated with increased knee laxity as well as decreased KOOS subscores (ie, quality of life and symptoms; R² > .12, P < .03). Postoperative notch width was not a significant predictor for any surgical outcome. None of the anatomic features were predictive of medial joint space width narrowing.

Conclusion:

Results partially support the hypothesis and highlight the importance of knee anatomy on several outcomes of ACL reconstruction among patients without subsequent graft or contralateral ACL injures. Increasing slopes in the coronal and sagittal planes with decreasing concavity of the medial tibial plateau lead to less favorable outcomes 7 years after surgery.

Keywords

ACL knee anatomy ACL reconstruction outcomes

Anterior cruciate ligament (ACL) reconstruction surgery has shown promising results in restoring the gross stability of a symptomatic ACL-deficient knee, but significant long-term problems affecting knee health and patient outcomes persist, including high rates of reinjury, poorer patient-reported outcomes, and a high risk for development of early-onset posttraumatic osteoarthritis (OA).^33,38,43 Accordingly, investigations of the factors affecting outcomes of ACL reconstruction are of great clinical significance to improve short- and long-term outcomes. The influence of various factors on ACL reconstruction outcomes—including those based on patients (eg, age, activity level, sport participation),^10,12,43 surgery (eg, graft type, size),^3,18,24,34 and rehabilitation (eg, neuromuscular and physical training)^22,37—has been the focus of many research efforts. In contrast, little is known about how a patient’s anatomic features of the knee joint may influence outcomes. A better understanding of the relationships between joint geometry and ACL outcomes would provide insight into which patients may or may not do well with surgical treatment.

The links between the complex morphological features of the tibiofemoral joint and its biomechanics (loads and motion) are well documented.^{20,27,35,36,46} Multiple anatomic indices, including tibial plateau morphology (posterior slope and concavity),^{4,21,31,36,48} tibial eminence size,⁴⁷ and femoral intercondylar notch size,^39,46,50 have been associated with increased ACL loading and risk of injury. Among those, there is strong evidence that posterior tibial slope (ie, the anterior elevation of the tibial plateau is greater than the posterior elevation)^4,19,21,31 and femoral notch width^39,46,50 are primary anatomic risk factors for ACL injuries. A few recent studies also investigated the effect of posterior tibial slope in the sagittal plane^{9,29,30,43,49} and notch width^29,30 on risk of secondary ACL injury. Despite the significance of reinjury after ACL reconstruction, particularly among adolescents, many patients do not have a reinjury. Therefore, it is important to understand if these anatomic features influence the outcomes of ACL reconstruction among patients who do not have a reinjury. Our objective was to test the associations between key anatomic features of the knee and clinically relevant outcomes of ACL reconstruction. We hypothesized that decreased postoperative femoral notch width, increased posterior and coronal slopes, and decreased concavity of the tibial plateau are associated with inferior clinical, patient-reported, and OA-related imaging outcomes 7 years after ACL reconstruction.

Methods

Participants

This study is based on a subset of participants enrolled in an ongoing clinical trial (NCT00434837) investigating the effects of initial graft tension on outcomes of ACL reconstruction with autograft.^1,18 The subset included those patients who did not have a subsequent graft or contralateral ACL failure after the index procedure, as determined by clinical examination and verified by magnetic resonance imaging (MRI), and those who were not lost to follow-up. The analyses presented here are unique and address hypotheses different from those of the original study.^1,18 The trial was approved by the institutional review board at Rhode Island Hospital, and all patients provided informed consent. Patients were recruited from the clinics of 3 surgeons (P.D.F., M.J.H., R.M.S.) over a 3-year period as previously described.^1,18 Inclusion criteria comprised an age range of 15 to 50 years, a Tegner activity score ≥2, and candidacy for unilateral patellar or hamstring tendon autograft reconstruction. Exclusion criteria were history of injury to either knee, evidence of knee OA on preoperative radiographs, diseases predisposing patients to articular cartilage damage, moderate-size fissures or lesions of the articular cartilage,¹⁶ meniscal tears involving greater than the central third of the meniscus, and increased laxity (grade >1) in the posterior cruciate ligament, medial collateral ligament, and lateral collateral ligament relative to the contralateral knee.^1,18 Of the 557 patients screened, 335 were excluded because they did not meet the inclusion criteria, and 112 patients declined participation, leaving 90 available for inclusion in the original trial.^1,18

ACL reconstruction was performed with a patellar tendon or 4-strand hamstring tendon autograft, the selection of which was based on surgeon and/or patient preference. A femoral notchplasty was routinely performed. All surgeons followed the same surgical technique in an effort to minimize variability.¹⁸ The original trial was designed to compare 2 graft tension protocols: 1 that restored anterior-posterior laxity to that of the contralateral leg (graft firmly tensioned with the knee at full extension; the low-tension treatment) and 1 that constrained knee laxity by 2 mm (graft firmly tensioned with the knee at 30° of flexion; the high-tension treatment), which were randomly assigned as previously described.¹⁸ Postoperatively, all patients followed a standardized rehabilitation program with the goal to return to sport at 6 months.^5,18 Multiple clinical, patient-reported, and imaging outcomes related to OA were measured at the 7-year postoperative follow-up visit. Patients were pooled for the current analysis, as both groups had similar outcomes.^1,18 However, the tension group was considered a potential explanatory variable.

Of the 90 patients enrolled in the trial, 53 had knee MRI at 3 years, a time point that a majority of patients first underwent MRI. Of these 53 patients, 44 had no subsequent injuries and completed their 7-year on-site visit. This subset of 44 patients had a mean ± SD age of 23.7 ± 9.2 years at the time of surgery and a mean baseline Tegner activity level of 5.6 ± 2.2. Twenty-eight (64%) were female; 24 (55%) had high-tension graft reconstruction; and 15 (34%) had hamstring tendon grafts.

Outcome Measures

The following outcomes, quantified at 7 years, were used in the current analyses.

Anterior-Posterior Knee Laxity

Anterior-posterior laxity values for both knees were measured with the KT-1000 Knee Arthrometer (MEDMetric Corporation) by a trained physical therapist.¹¹ Three manual maximum tests were performed and the displacement readings averaged. The difference between legs (surgical knee – contralateral intact knee) was calculated and used for the analysis.

Knee injury and Osteoarthritis Outcome Score

The Knee injury and Osteoarthritis Outcome Score (KOOS)⁴¹ was implemented to assess patient-reported outcomes. The KOOS evaluates 5 domains: knee-related quality of life (QOL), sports and recreation function, activities of daily living, symptoms, and pain. The subscores were presented on a scale ranging from 0 to 100, with 100 indicating a perfect knee.

Medial Joint Space Width

Medial minimum joint space width measurements were obtained from standardized radiographs with the semiflexed metatarsophalangeal view.^8,18 The minimum joint space width of the medial compartment was calculated with a validated semiautomated algorithm.^14,15 The difference in medial joint space width between legs (surgical knee – contralateral intact knee) was calculated and used for this analysis.

Osteoarthritis Research Society International Radiographic Score

The overall condition of the joint was assessed with the modified Osteoarthritis Research Society International (OARSI) radiographic grading scale.² With posterior-anterior and lateral radiographs of both knees, a grade of 0 (normal) to 4 (severe) was assigned to 2 radiographic features: osteophyte formation and joint space narrowing. In addition, sclerosis, attrition, and ligament calcification were assessed on a dichotomous scale. An experienced musculoskeletal radiologist scored all films while blinded to other patient factors. The difference in OARSI score between legs (surgical knee – contralateral intact knee) was calculated and used for the analysis.

Anatomic Predictors

Patients were scanned with a 3T scanner (Tim Trio; Siemens) and a surface knee coil per a standardized protocol, with acquisition parameters based on a 3-dimensional T1-weighted FLASH sequence (ie, fast low-angle shot; repetition time/echo time/flip angle: 20 milliseconds/7.6 milliseconds/12°; field of view: 160 mm; matrix: 512 × 512 pixels, slice thickness/gap: 1.5/0 mm). These images were used to quantify several anatomic features of the femoral condyles and tibial plateau (Figure 1). A single examiner (D.S.Y.) performed the anatomic measurements while blinded to the patient’s identity. To assess the reliability of the measurements, a subset of images was randomly selected (n = 20) and blindly analyzed by another independent examiner (A.M.K.). Variance component analysis was performed to calculate the intraclass correlation coefficients (ICCs) for each quantified anatomic index.¹⁷

Femoral Notch Width

Width of the femoral notch was measured in the coronal plane, parallel to a line along the most inferior aspects of the femoral condyles.³⁹ The measurement was done at the middle of the ACL attachment.⁵⁰ The ICC for notch width was 0.912.

Posterior Tibial Slope

The posterior slopes of the medial and lateral tibial plateaus were measured with the techniques described by Hudek et al.²³ Briefly, a central sagittal slice was selected in which the tibial attachment of the posterior cruciate ligament, the intercondylar eminence, and the anterior and posterior tibial cortices appeared in a concave shape. Then, 1 cranial circle (touching the anterior, posterior, and cranial tibial cortex) and 1 caudal circle (touching the anterior and posterior cortex) were fitted to the tibial head. The line connecting the center of 2 circles was defined as the longitudinal tibial axis.²³ This technique was shown to be highly repeatable and independent of the proximal tibial length covered in MRI.³² The posterior slope of the tibial plateau was meaured in a sagittal slice at the center of each medial and lateral plateau as the angle between a line that joined the peak points on the anterior and posterior rims of the plateau and a line perpendicular to the longitudinal axis of the tibia.²⁰ This method was shown to be able to quantify the tibial slope with a sensitivity of 1°.²¹ The ICCs for the posterior tibial slope were 0.830 (medial) and 0.890 (lateral).

Coronal Tibial Slope

The slope of the tibial plateau in the coronal plane was measured with the technique described by Hashemi et al.²⁰ Briefly, the longitudinal axis of the tibia was established in the coronal slice passing through the approximate centroid of the tibial plateau. This was done by determining the midpoint of the medial-to-lateral width of the tibia at 2 points located approximately 4 to 5 cm apart and as distally in the image as possible. The extended line connecting the 2 midpoints represents the longitudinal (or diaphyseal) axis of the tibia in the coronal plane. The coronal slope of the tibial plateau was then measured as the angle between a line joining the peak points on the medial and lateral aspects of the plateau and the line perpendicular to the longitudinal axis.²⁰ The ICC for the coronal tibial slope was 0.933.

Medial Tibial Depth

The medial tibial depth was measured as the perpendicular distance between a line connecting the anterior and posterior rims of the medial tibial plateau and the deepest point of the medial plateau in the same slice that the medial slope was measured.²⁰ The ICC for the medial tibial depth was 0.849.

Statistical Analyses

Simple linear regression analyses were performed to investigate the relationships between each of the anatomic predictors and surgical outcome measures at 7 years (bivariate analyses). Additionally, stepwise regression analyses were used to identify the best predictive models for each surgical outcome. For the stepwise procedure, all anatomic and potentially important demographic variables (ie, sex, graft type, age, and tension group) were considered candidates for inclusion in the model. Statistical analyses were conducted by a senior biostatistician (G.J.B.) with SAS statistical software (v 9.4; SAS Institute Inc). Statistical significance was based on α = .05.

Results

Descriptive statistics for the anatomic measures and 7-year surgical outcomes are presented in Table 1. Except for the posterior slopes of the medial and lateral tibial plateaus (R² = .62, P < .001), there were no significant correlations among the potential anatomic predictors (R² < .08, P > .05) (Appendix Figure A1, available in the online version of this article).

Table 1

Descriptive Statistics of the Anatomic Predictors and Surgical Outcomes at 7-Year Follow-up^a

	Mean ± SD	Range
Predictors
NW, mm	17.5 ± 3.1	12.1 to 24.6
LTS, deg	6.6 ± 2.2	2.1 to 13.4
MTS, deg	4.7 ± 1.9	0.2 to 7.3
CTS, deg	2.9 ± 2.1	−1.2 to 8.8
MTD, mm	2.1 ± 0.7	0.9 to 3.6
Outcomes
AP knee laxity,^b mm	1.6 ± 3.0	−6.0 to 8.3
KOOS
QOL	76.2 ± 22.7	6.3 to 100.0
Sports	82.3 ± 19.3	20.0 to 100.0
ADL	94.1 ± 10.6	52.9 to 100.0
Symptoms	80.1 ± 16.8	32.1 to 100.0
Pain	88.8 ± 20.0	11.1 to 100.0
Medial mJSW,^b mm	−0.1 ± 0.7	−2.5 to 1.2
OARSI x-ray score ^b	0.8 ± 2.3	−2.0 to 13.0

ACL, anterior cruciate ligament; ADL, activities of daily living; AP, anteroposterior; CTS, coronal tibial slope; KOOS, Knee injury and Osteoarthritis Outcome Score; LTS, lateral tibial slope; mJSW, medial joint space width; MTD, medial tibial depth; MTS, medial tibial slope; NW, notch width; OARSI, Osteoarthritis Research Society International; QOL, quality of life.

Presented as the difference between the surgical leg and the contralateral ACL-intact leg (surgical – contralateral).

Bivariate Associations Between Anatomic Measures and 7-Year Surgical Outcomes

Postoperative notch width was not a significant predictor for any of the surgical outcomes at 7 years (R² < .04 and P > .2; Appendix Table A1, available online).

Increased posterior slope of the lateral tibial plateau was associated with increased side-to-side difference in knee laxity, decreased KOOS subscores, and increased side-to-side difference in the OARSI x-ray score at 7 years after ACL reconstruction. Lateral tibial slope explained between 11% and 18% of the observed variability in knee laxity, KOOS subscores, and OARSI x-ray score. On average, every degree increase in lateral tibial slope was linked to increased side-to-side differences in knee laxity by 0.4 mm, decreased KOOS subscores by 1 to 4 points, and increased side-to-side differences in the OARSI x-ray score by 0.4 points (Table 2).

Table 2

Regression Coefficients for Lateral Tibial Slope Predicting Each Surgical Outcome at 7 Years^a

Outcome	β (95% CI)	R ²	P Value
AP knee laxity^b	0.4 (0.0 to 0.8)	.11	.044
KOOS
QOL	−4.3 (–7.2 to –1.5)	.18	.004
Sports	−3.2 (–5.7 to –0.8)	.14	.013
ADL	−1.8 (–3.1 to –0.4)	.14	.014
Symptoms	−2.8 (–5.0 to –0.7)	.14	.013
Pain	−3.3 (–5.9 to –0.7)	.14	.014
Medial mJSW^b	−0.1 (–0.2 to 0.1)	.02	.395
OARSI x-ray score^b	0.4 (0.1 to 0.7)	.15	.012

Significant associations are highlighted in bold, P < .05. ACL, anterior cruciate ligament; ADL, activities of daily living; AP, anteroposterior; KOOS, Knee injury and Osteoarthritis Outcome Score; mJSW, medial joint space width; OARSI, Osteoarthritis Research Society International; QOL, quality of life.

Presented as the difference between the surgical leg and the contralateral ACL-intact leg (surgical – contralateral).

Increased posterior slope of the medial tibial plateau was associated with a lower KOOS and a higher side-to-side difference in the OARSI x-ray score at 7 years. Medial tibial slope explained between 12% and 25% of the variations in KOOS and OARSI x-ray score. On average, every degree increase in medial tibial slope was linked to a deceased KOOS by 2 to 6 points and an increased side-to-side difference in the OARSI x-ray score by 0.4 points (Table 3).

Table 3

Regression Coefficients for Medial Tibial Slope Predicting Each Surgical Outcome at 7 Years^a

Outcome	β (95% CI)	R ²	P Value
AP knee laxity^b	0.4 (–0.1 to 0.9)	.05	.155
KOOS
QOL	−5.8 (−9.0 to −2.7)	.25	<.001
Sports	−4.5 (–7.3 to –1.8)	.20	.002
ADL	−1.9 (–3.5 to –0.3)	.12	.020
Symptoms	−3.6 (–6.1 to –1.1)	.17	.006
Pain	−3.6 (–6.6 to –0.6)	.12	.020
Medial mJSW^b	0.0 (–0.1 to 0.1)	.00	.925
OARSI x-ray score^b	0.4 (0.1 to 0.8)	.12	.028

Presented as the difference between the surgical leg and the contralateral ACL-intact leg (surgical – contralateral).

Increased slope of the tibial plateau in coronal plane was associated with lower KOOS subscores at 7 years. Coronal tibial slope explained between 12% and 27% of the variability in KOOS subscores. On average, every degree increase in coronal tibial slope was linked to decreased KOOS subscores by 2 to 5 points (Table 4). Additionally, there was some evidence that increased coronal tibial slope was associated with an increased OARSI x-ray score (P = .079).

Table 4

Regression Coefficients for Coronal Tibial Slope Predicting Each Surgical Outcome at 7 Years^a

Outcome	β (95% CI)	R ²	P Value
AP knee laxity^b	0.2 (–0.2 to 0.7)	.03	.309
KOOS
QOL	−4.3 (−7.4 to −1.1)	.16	.010
Sports	−4.5 (–7.0 to –1.9)	.23	.001
ADL	−2.6 (–4.0 to –1.2)	.27	<.001
Symptoms	−2.8 (–5.2 to –0.4)	.12	.024
Pain	−4.9 (–7.6 to –2.4)	.27	<.001
Medial mJSW^b	0.0 (–0.1 to 0.1)	.01	.599
OARSI x-ray score^b	0.3 (0.0 to 0.7)	.08	.079

Presented as the difference between the surgical leg and the contralateral ACL-intact leg (surgical – contralateral).

Decreased maximum depth of the medial tibial plateau (shallow plateau) was associated with increased knee laxity as well as decreased KOOS QOL and symptoms subscores. Medial tibial depth explained 13% to 23% of the variability in knee laxity and the KOOS QOL and symptoms subscores. On average, every millimeter decrease in medial tibial depth was linked to increased side-to-side difference in knee laxity by 1.6 mm as well as decreased KOOS QOL and symptoms subscores by 16 and 12 points, respectively (Table 5).

Table 5

Coefficients Associated With Medial Tibial Depth for Predicting Surgical Outcomes at 7 Years

Outcome	β (95% CI)	R ²	P Value
AP knee laxity^b	−1.6 (–2.9 to –0.2)	.13	.028
KOOS
QOL	16.1 (6.8 to 25.4)	.23	.001
Sports	5.4 (–3.1 to 13.9)	.04	.210
ADL	3.9 (–0.8 to 8.7)	.06	.106
Symptoms	11.8 (4.7 to 18.7)	.22	.002
Pain	7.5 (–1.6 to 16.5)	.06	.106
Medial mJSW^b	−0.2 (–0.5 to 0.2)	.02	.395
OARSI x-ray score^b	−0.4 (–1.5 to 0.6)	.02	.430

Presented as the difference between the surgical leg and the contralateral ACL-intact leg (surgical – contralateral).

Stepwise Regression With Anatomic and Demographics Measures as Potential Predictors

The results of the stepwise regression models for each surgical outcome are presented in Table 6. The derived prediction model for knee laxity included only the medial tibial depth, explaining 19% of the variation in side-to-side difference in knee laxity. The model predicting the KOOS QOL subscore included sex, medial tibial slope, and medial tibial depth. Combinations of these 3 parameters explained 42% of the observed variation in the KOOS QOL subscore. The combination of sex, graft type, and medial and coronal tibial slopes produced the predictive model of the KOOS sports subscore and explained 54% of the variation in this outcome. The KOOS subscore related to activities of daily living was predicted by a combination of sex, graft type, and lateral and coronal tibial slopes. These 4 parameters explained 54% of the variation observed in this outcome. The model to predict the KOOS symptoms subscore included graft type, lateral tibial slope, and medial tibial depth, which explained 45% of the variation in the KOOS symptoms subscore. The combination of sex, graft type, and lateral and coronal tibial slopes was best predictive of the KOOS pain subscore and explained 54% of the variation in this outcome. None of the studied anatomic features were predictive of medial joint space width narrowing at 7 years. However, lateral tibial slope was the only predictor of the OARSI x-ray score in the stepwise analysis and explained 15% of the side-to-side difference at 7 years.

Table 6

Stepwise Regression Analysis Indicating Significant Predictors of Surgical Outcomes in a Multivariate Model With the Demographic Variables Included^a

		Sex (male)		Graft Type (Hamstring)		LTS		MTS		CTS		MTD
Outcome	Intercept	β (95% CI)	P Value	β (95% CI)	P Value	β (95% CI)	P Value	β (95% CI)	P Value	β (95% CI)	P Value	β (95% CI)	P Value	Model R²
AP knee laxity^b	5.5											−1.9 (–3.2 to 0.6)	.006	.19
KOOS
QOL	70.8	−13.5 (−25.7 to −1.3)	.034					−4.5 (−7.6 to −1.4)	.002			15.1 (6.1 to 24.2)	.009	.42
Sports	109.7	−10.4 (−20.0 to −0.9)	.034	11.9 (2.5 to 21.4)	.015			−3.5 (−5.9 to −1.1)	.006	−4.2 (−6.4 to −2.1)	<.001			.54
ADL	110.4	−5.9 (−11.2 to −0.5)	.007	6.9 (1.5 to 12.3)	.045	−1.4 (−2.6 to −0.3)	.016			−2.55 (−3.7 to −1.4)	<.001			.54
Symptoms	68.9			13.8 (5.1 to 22.6)	.014	−2.7 (−4.6 to −0.9)	.006					12.3 (5.9 to 18.6)	<.001	.45
Pain	119.7	−11.1 (−21.2 to −1.0)	.035	13.0 (2.8 to 23.2)	.015	−2.7 (−4.9 to −0.6)	.016			−4.8 (−7.0 to −2.6)	<.001			.54
OARSI x-ray score^b	−1.8					0.4 (0.1 to 0.7)	.017							.15

Notch width was not considered, as it was not significant in any of the univariate analyses. Medial joint space width was not included in the table, as it was not significant in any of the univariate analyses. ACL, anterior cruciate ligament; ADL, activities of daily living; AP, anteroposterior; CTS, coronal tibial slope; KOOS, Knee injury and Osteoarthritis Outcome Score; LTS, lateral tibial slope; mJSW, medial joint space width; MTD, medial tibial depth; MTS, medial tibial slope; OARSI, Osteoarthritis Research Society International; QOL, quality of life.

Presented as the difference between the surgical leg and the contralateral ACL-intact leg (surgical – contralateral).

Discussion

We determined that knee laxity, the KOOS subscores, and the OARSI x-ray score were influenced by the slopes of the tibial plateau in the coronal and sagittal planes and the maximum depth of the medial tibial plateau 7 years after ACL reconstruction. The finding that these anatomic features, except for medial and lateral tibial slopes, were not correlated with one another suggests that they independently influence ACL reconstruction outcomes. Contrary to our hypotheses, we did not find any associations between postoperative femoral notch width and any of the surgical outcomes or between the anatomic features and minimum joint space width in the medial compartment. Therefore, these results partially support our hypothesis and highlight the importance of knee anatomy on several outcomes of ACL reconstruction among patients without subsequent graft or contralateral ACL injures.

Patients with steep posterior slope of the lateral tibial plateau had inferior outcomes with regard to increased knee laxity, decreased KOOS subscores, and increased OARSI score. During weightbearing tasks, posterior tibial slope produces an anterior shear force component as an axial compression force is applied across the knee joint.¹⁹ Accordingly, an increased posterior tibial slope would lead to an increased anterior tibial shear force,³⁵ anterior tibial acceleration and translation,³⁶ and ACL strain.^31,36 Posterior tibial slope has also been shown to contribute to knee rotation in coronal (abduction)²⁷ and axial (internal tibial rotation)^20,46 planes, which both can increase ACL loading.^25,40 Several groups have shown significant increases in risk of graft failure among patients with steep lateral tibial slope.^{9,29,30,43,49} Our current findings suggest that while this increased ACL loading can lead to graft failure under injurious conditions, it may also result in inferior graft properties by overloading the healing tissue of patients who do not rupture their graft. The inferior graft properties could ultimately lead to unsatisfactory outcomes—in particular, increased residual knee laxity.⁶ Increased knee laxity can also result in inferior knee function⁷ and increased cartilage degeneration in the long term,²⁶ which could lead to unsatisfactory KOOS subscores and an elevated OARSI x-ray score, as seen here.

Likewise, the posterior slope of the medial tibial plateau has also been shown to contribute to anterior shear loading and joint rotation as well as ACL loading and risk of injury.^20,21,27,46 Thus, it is possible that increased medial tibial slope can overload the healing graft and ultimately result in unfavorable outcomes as suggested here. Increased medial tibial slope was also demonstrated to result in increased cartilage loading under weightbearing conditions.²⁸ The combination of these effects can be manifested as inferior joint function and increased pain and joint degeneration, as reported here by decreased KOOS subscores and an increased OARSI x-ray score. Given the strong correlations between medial and lateral tibial slopes,²⁰ it is possible that observed associations between medial tibial slope and surgical outcomes are influenced by the lateral tibial slope. However, the stepwise analysis highlights the distinct effects, with the medial tibial slope influencing the KOOS QOL and sports subscores and the lateral tibial slope influencing KOOS daily activities, symptoms, and pain subscores with the OARSI score. The reasons for this are unclear and require further study.

Coronal tibial slope (the slope from the lateral edge of the tibial plateau to the medial edge) has been shown to influence knee rotations in the coronal and axial planes.⁴⁵ A positive slope represents a more elevated lateral tibial plateau than medial in the coronal plane. A greater coronal tibial slope has been associated with greater internal tibial rotation excursions, while a lower coronal tibial slope was linked to greater knee valgus.⁴⁵ Although coronal tibial slope has not been shown to influence the risk of ACL injury, it is possible that excessive internal rotation and varus alignment in knees with high coronal tibial slope could lead to increased cartilage wear and degeneration. A recent study demonstrated a significant association between increased coronal tibial slope and increased risk of accelerated knee OA.¹³ Our observations of decreased KOOS subscores and a trend toward increased OARSI scores among patients with high coronal tibial slopes reinforce the importance of the coronal tibial slope and its potential effect in increased risk of posttraumatic OA. The importance of the coronal tibial slope on ACL reconstruction outcomes is further supported by the stepwise analysis indicating coronal tibial slope as a significant predictor of KOOS outcomes related to sports, daily activities, and pain.

The maximum depth of the medial tibial plateau has been suggested as a surrogate for the extent of medial tibial plateau concavity.^20,21 A deeper (more concave) medial tibial plateau will constrain the femoral condyle to a greater extent and may result in increased resistance to displacement of the tibia relative to the femur.²⁰ Conversely, knees with a shallower medial tibial plateau may be more prone to anterior-directed translation of the tibia. Prior studies demonstrated significantly lower medial tibial depth among patients with an injured ACL as compared with matched uninjured controls.²¹ A flatter medial tibial plateau can also result in increased medial cartilage pressure, possibly owing to less congruency and a smaller contact area between the curved femoral condyle and flat tibial plateau.²⁸ This increased instability can lead to higher residual knee laxity, which may in turn contribute to a symptomatic knee and lower QOL, especially in the presence of excessive cartilage loading and possible degeneration. The importance of medial tibial depth on anterior-posterior knee stability is highlighted by our stepwise analysis indicating that medial tibial depth is the sole predictor of the side-to-side differences in knee laxity at 7 years.

Interestingly, we did not see any associations between postoperative notch width and the outcomes of ACL reconstruction studied here. Given that a notchplasty (notch enlargement) is commonly performed during ACL reconstruction surgery, the effect of notch width on outcomes in the present study was likely minimized. Further studies are warranted to investigate if preoperative notch width can influence ACL reconstruction outcomes.

None of the studied outcomes were associated with minimum joint space width in the medial compartment. Structural assessments of joint space width via radiography are not very sensitive measures to detect changes in the early stages of OA,³⁶ which may have contributed to the observed lack of association. However, we identified significant associations between the anatomic features and the OARSI x-ray score, which focuses on degeneration of the whole joint and not just cartilage thickness. It is possible that we would see relationships between the anatomic features and joint space width at later follow-up times after significant narrowing occurs.

There are several limitations to consider. Although the data were prospectively collected, the study was retrospective in that the research question was asked after the data were acquired. The bony features were measured from MRI acquired 3 years postoperatively, as preoperative images were not available for all patients. Therefore, we assumed that the bony features of the joint would not have changed since the injury. Despite relatively high follow-up rates, MRI at 3 years was available for only a subset of patients, as MRI was added to the parent trial after 50% of the patients were enrolled, reducing our sample size with MRI to 44, which in turn reduced the power of the study. Our study was 80% powered to detect anatomic measures explaining ≥18% of the variability in surgical outcomes. Finally, given the available number of cases, male and female patients of all ages with different graft types (patellar tendon and hamstring tendon autografts) and tension conditions (tensioned to restore normal knee laxity or overconstrain knee laxity) were pooled together, instead of separated into subgroup analyses, which may have affected our findings. To minimize these potential effects and to confirm our observations in the bivariate analyses, we included these 4 demographic factors in our stepwise analyses. Graft tension was not a significant contributor to the models, which is in agreement with our previous observations indicating minimal graft tension effects on outcomes at 7-year follow-up.¹ While young age has been associated with higher rates of graft failure,⁴³ ACL reconstruction outcomes were shown to be comparable across age groups of patients without subsequent injury.^10,12 This is in agreement with our observations of age not being significant in any of the stepwise models. Controversies exist on the effect of graft type (ie, hamstrings vs quadriceps) and sex on the outcomes of ACL reconstruction, with some studies suggesting significant effects and others demonstrating comparable outcomes.^42,44 Sex and graft type were significant contributors to some of the stepwise models. However, any conclusions regarding their role would be premature, particularly given the lack of associations between sex and graft type with the studied outcomes in a bivariate setting (P > .05 for all associations).

In conclusion, we determined that tibial slope in the sagittal and coronal planes and concavity of tibial plateau significantly influenced several of the clinical, patient-reported, and imaging outcomes related to posttraumatic OA of ACL reconstruction. Increasing slopes in the coronal and sagittal planes with decreasing concavity of the medial tibial plateau lead to less favorable outcomes. The study provides a better understanding of the effect of bony geometry on ACL reconstruction outcomes, which may help clinicians inform patients and could potentially be used to guide rehabilitation and return-to-play decisions.

Supplemental Material

DS_10.1177_0363546518823556 – Supplemental material for Anatomic Features of the Tibial Plateau Predict Outcomes of ACL Reconstruction Within 7 Years After Surgery

Supplemental material, DS_10.1177_0363546518823556 for Anatomic Features of the Tibial Plateau Predict Outcomes of ACL Reconstruction Within 7 Years After Surgery by Ata M. Kiapour, Daniel S. Yang, Gary J. Badger, Naga Padmini Karamchedu, Martha M. Murray, Paul D. Fadale, Michael J. Hulstyn, Robert M. Shalvoy and Braden C. Fleming in The American Journal of Sports Medicine

Footnotes

Acknowledgements

The research reported in this publication was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health (R01-AR047910, R01-AR065462), the Lucy Lippitt Endowment, the RIH Orthopaedic Foundation, the Boston Children’s Hospital Orthopaedic Surgery Foundation, and the National Football League Players Association through the Harvard Catalyst’s Football Players Health Study.

The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of the funding agencies.

One or more of the authors has declared the following potential conflict of interest or source of funding: This study was supported by the National Institutes of Health (R01-AR047910) and internal department funds. M.M.M. is a founder and equity holder of MIACH Orthopaedics and receives royalties from Springer. M.J.H. receives hospitality payments from Arthrex and compensation other than consulting from Smith & Nephew. R.M.S. has received hospitality payments from Stryker, consulting fees from Medical Device Business Services and DePuy, and education payments from Arthrex. B.C.F. is a founder of MIACH Orthopaedics and a consultant for NY R&D Center for Translational Medicine and receives travel support from Smith & Nephew and royalties from Springer. 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.

References

Akelman

Fadale

Hulstyn

et al . Effect of matching or overconstraining knee laxity during anterior cruciate ligament reconstruction on knee osteoarthritis and clinical outcomes: a randomized controlled trial with 84-month follow-up. Am J Sports Med. 2016;44:1660-1670.

Altman

Gold

GE.

Atlas of individual radiographic features in osteoarthritis, revised. Osteoarthritis Cartilage. 2007;15:A1-A56.

Amendola

Menon

Clatworthy

Fowler

PJ.

The effect of fixation technique on graft position in anterior cruciate ligament reconstruction. Iowa Orthop J. 2003;23:29-35.

Beynnon

Hall

Sturnick

et al . Increased slope of the lateral tibial plateau subchondral bone is associated with greater risk of noncontact ACL injury in females but not in males: a prospective cohort study with a nested, matched case-control analysis. Am J Sports Med. 2014;42:1039-1048.

Beynnon

Johnson

et al . Rehabilitation after anterior cruciate ligament reconstruction: a prospective, randomized, double-blind comparison of programs administered over 2 different time intervals. Am J Sports Med. 2005;33:347-359.

Biercevicz

Akelman

Fadale

et al . MRI volume and signal intensity of ACL graft predict clinical, functional, and patient-oriented outcome measures after ACL reconstruction. Am J Sports Med. 2015;43:693-699.

Brandsson

Karlsson

Sward

Kartus

Eriksson

Karrholm

Kinematics and laxity of the knee joint after anterior cruciate ligament reconstruction: pre- and postoperative radiostereometric studies. Am J Sports Med. 2002;30:361-367.

Buckland-Wright

Wolfe

Ward

RJ.

Substantial superiority of semiflexed (MTP) views in knee osteoarthritis: a comparative radiographic study, without fluoroscopy, of standing extended, semiflexed (MTP), and schuss views. J Rheumatol. 1999;26:2664-2674.

Christensen

Krych

Engasser

Vanhees

Collins

Dahm

DL.

Lateral tibial posterior slope is increased in patients with early graft failure after anterior cruciate ligament reconstruction. Am J Sports Med. 2015;43:2510-2514.

10.

Cinque

Chahla

Moatshe

et al . Outcomes and complication rates after primary anterior cruciate ligament reconstruction are similar in younger and older patients. Orthop J Sports Med. 2017;5:2325967117729659.

11.

Daniel

Malcom

Losse

Stone

Sachs

Burks

RT.

Instrumented measurement of anterior laxity of the knee. J Bone Joint Surg Am. 1985;67:720-726.

12.

Desai

Bjornsson

Samuelsson

Karlsson

Forssblad

Outcomes after ACL reconstruction with focus on older patients: results from the Swedish National Anterior Cruciate Ligament Register. Knee Surg Sports Traumatol Arthrosc. 2014;22:379-386.

13.

Driban

Stout

Duryea

et al . Coronal tibial slope is associated with accelerated knee osteoarthritis: data from the Osteoarthritis Initiative. BMC Musculoskelet Disord. 2016;17:299.

14.

Duryea

Peterfy

Gordon

Genant

HK.

Trainable rule-based algorithm for the measurement of joint space width in digital radiographic images of the knee. Med Phys. 2000;27:580-591.

15.

Duryea

Neumann

Niu

et al . Comparison of radiographic joint space width with magnetic resonance imaging cartilage morphometry: analysis of longitudinal data from the Osteoarthritis Initiative. Arthritis Care Res (Hoboken). 2010;62:932-937.

16.

Dwyer

Martin

Kendra

et al . Reliability and validity of the Arthroscopic International Cartilage Repair Society Classification System: correlation with histological assessment of depth. Arthroscopy. 2017;33:1219-1224.

17.

Eliasziw

Young

Woodbury

Fryday-Field

Statistical methodology for the concurrent assessment of interrater and intrarater reliability: using goniometric measurements as an example. Phys Ther. 1994;74:777-788.

18.

Fleming

Fadale

Hulstyn

et al . The effect of initial graft tension after anterior cruciate ligament reconstruction: a randomized clinical trial with 36-month follow-up. Am J Sports Med. 2013;41:25-34.

19.

Giffin

Vogrin

Zantop

Woo

Harner

CD.

Effects of increasing tibial slope on the biomechanics of the knee. Am J Sports Med. 2004;32:376-382.

20.

Hashemi

Chandrashekar

Gill

et al . The geometry of the tibial plateau and its influence on the biomechanics of the tibiofemoral joint. J Bone Joint Surg Am. 2008;90:2724-2734.

21.

Hashemi

Chandrashekar

Mansouri

et al . Shallow medial tibial plateau and steep medial and lateral tibial slopes: new risk factors for anterior cruciate ligament injuries. Am J Sports Med. 2010;38:54-62.

22.

Hewett

Di Stasi

Myer

GD.

Current concepts for injury prevention in athletes after anterior cruciate ligament reconstruction. Am J Sports Med. 2013;41:216-224.

23.

Hudek

Schmutz

Regenfelder

Fuchs

Koch

PP.

Novel measurement technique of the tibial slope on conventional MRI. Clin Orthop Relat Res. 2009;467:2066-2072.

24.

Hussein

van Eck

Cretnik

Dinevski

FH.

Prospective randomized clinical evaluation of conventional single-bundle, anatomic single-bundle, and anatomic double-bundle anterior cruciate ligament reconstruction: 281 cases with 3- to 5-year follow-up. Am J Sports Med. 2012;40:512-520.

25.

Kiapour

Demetropoulos

Kiapour

et al . Strain response of the anterior cruciate ligament to uniplanar and multiplanar loads during simulated landings: implications for injury mechanism. Am J Sports Med. 2016;44:2087-2096.

26.

Kiapour

Fleming

Murray

MM.

Structural and anatomic restoration of the anterior cruciate ligament is associated with less cartilage damage 1 year after surgery: healing ligament properties affect cartilage damage. Orthop J Sports Med. 2017;5:2325967117723886.

27.

Kiapour

Goel

et al . Uni-directional coupling between tibiofemoral frontal and axial plane rotation supports valgus collapse mechanism of ACL injury. J Biomech. 2015;48:1745-1751.

28.

Kiapour

Goel

Hewett

Demetropoulos

CK.

The effects of tibiofemoral joint subchondral bone anatomy on medial cartilage loading: implications for knee osteoarthritis risk. Trans Orthop Res Soc. 2016;41:0225.

29.

Levins

Argentieri

Sturnick

et al . Geometric characteristics of the knee are associated with a noncontact ACL injury to the contralateral knee after unilateral ACL injury in young female athletes. Am J Sports Med. 2017;45:3223-3232.

30.

Levins

Sturnick

Argentieri

et al . Geometric risk factors associated with noncontact anterior cruciate ligament graft rupture. Am J Sports Med. 2016;44:2537-2545.

31.

Lipps

Ashton-Miller

Wojtys

EM.

Morphologic characteristics help explain the gender difference in peak anterior cruciate ligament strain during a simulated pivot landing. Am J Sports Med. 2012;40:32-40.

32.

Lipps

Wilson

Ashton-Miller

Wojtys

EM.

Evaluation of different methods for measuring lateral tibial slope using magnetic resonance imaging. Am J Sports Med. 2012;40:2731-2736.

33.

Lohmander

Englund

Dahl

Roos

EM.

The long-term consequence of anterior cruciate ligament and meniscus injuries: osteoarthritis. Am J Sports Med. 2007;35:1756-1769.

34.

MARS Group. Effect of graft choice on the outcome of revision anterior cruciate ligament reconstruction in the Multicenter ACL Revision Study (MARS) Cohort. Am J Sports Med. 2014;42:2301-2310.

35.

McLean

Lucey

Rohrer

Brandon

Knee joint anatomy predicts high-risk in vivo dynamic landing knee biomechanics. Clin Biomech (Bristol, Avon). 2010;25:781-788.

36.

McLean

Palmer

et al . The relationship between anterior tibial acceleration, tibial slope, and ACL strain during a simulated jump landing task. J Bone Joint Surg Am. 2011;93:1310-1317.

37.

Nagelli

Wordeman

Di Stasi

Hoffman

Marulli

Hewett

TE.

Biomechanical deficits at the hip in athletes with ACL reconstruction are ameliorated with neuromuscular training. Am J Sports Med. 2018;46(11):2772-2779.

38.

Oiestad

Holm

Aune

et al . Knee function and prevalence of knee osteoarthritis after anterior cruciate ligament reconstruction: a prospective study with 10 to 15 years of follow-up. Am J Sports Med. 2010;38:2201-2210.

39.

Park

Nam

Kim

Hwang

SC.

Measurement of knee morphometrics using MRI: a comparative study between ACL-injured and non-injured knees. Knee Surg Relat Res. 2012;24:180-185.

40.

Quatman

Kiapour

Demetropoulos

et al . Preferential loading of the ACL compared with the MCL during landing: a novel in sim approach yields the multiplanar mechanism of dynamic valgus during ACL injuries. Am J Sports Med. 2014;42:177-186.

41.

Roos

Lohmander

Ekdahl

Beynnon

BD.

Knee injury and Osteoarthritis Outcome Score (KOOS)—development of a self-administered outcome measure. J Orthop Sports Phys Ther. 1998;28:88-96.

42.

Ryan

Magnussen

Cox

Hurbanek

Flanigan

Kaeding

CC.

ACL reconstruction: do outcomes differ by sex? A systematic review. J Bone Joint Surg Am. 2014;96:507-512.

43.

Salmon

Heath

Akrawi

Roe

Linklater

Pinczewski

LA.

20-year outcomes of anterior cruciate ligament reconstruction with hamstring tendon autograft: the catastrophic effect of age and posterior tibial slope. Am J Sports Med. 2018;46:531-543.

44.

Samuelsson

Andersson

Karlsson

Treatment of anterior cruciate ligament injuries with special reference to graft type and surgical technique: an assessment of randomized controlled trials. Arthroscopy. 2009;25:1139-1174.

45.

Shultz

Schmitz

RJ.

Tibial plateau geometry influences lower extremity biomechanics during landing. Am J Sports Med. 2012;40:2029-2036.

46.

Simon

Everhart

Nagaraja

Chaudhari

AM.

A case-control study of anterior cruciate ligament volume, tibial plateau slopes and intercondylar notch dimensions in ACL-injured knees. J Biomech. 2010;43:1702-1707.

47.

Sturnick

Argentieri

Vacek

et al . A decreased volume of the medial tibial spine is associated with an increased risk of suffering an anterior cruciate ligament injury for males but not females. J Orthop Res. 2014;32:1451-1457.

48.

Sturnick

Van Gorder

Vacek

et al . Tibial articular cartilage and meniscus geometries combine to influence female risk of anterior cruciate ligament injury. J Orthop Res. 2014;32:1487-1494.

49.

Webb

Salmon

Leclerc

Pinczewski

Roe

JP.

Posterior tibial slope and further anterior cruciate ligament injuries in the anterior cruciate ligament-reconstructed patient. Am J Sports Med. 2013;41:2800-2804.

50.

Whitney

Sturnick

Vacek

et al . Relationship between the risk of suffering a first-time noncontact ACL injury and geometry of the femoral notch and ACL: a prospective cohort study with a nested case-control analysis. Am J Sports Med. 2014;42:1796-1805.

Supplementary Material

Please find the following supplemental material available below.

For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.

For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.

0.00 MB

0.58 MB