Twenty-Year Outcomes of a Longitudinal Prospective Evaluation of Isolated Endoscopic Anterior Cruciate Ligament Reconstruction With Patellar Tendon Autografts

Abstract

Background:

Long-term prospective follow-up studies of single-incision endoscopic anterior cruciate ligament (ACL) reconstruction are limited and may include confounding factors.

Purpose:

This longitudinal prospective study reports the outcomes of isolated ACL reconstruction using middle-third patellar tendon autografts in 90 patients over 20 years.

Study Design:

Case series; Level of evidence, 4.

Methods:

Between January 1993 and April 1994, a total of 90 patients met study inclusion criteria: evaluation at 1, 2, 3, 4, 5, 7, 10, 15, and 20 years after surgery. Exclusion criteria were associated ligamentous injuries requiring surgery, previous meniscectomy or meniscal injuries requiring more than one-third meniscectomy, chondral injuries, and an abnormal contralateral knee.

Results:

At 20 years, 32 (36%) patients had sustained another ACL injury: 8 (9%) to the index limb and 27 (30%) to the contralateral limb (3 injuring both knees). The mean International Knee Documentation Committee (IKDC) score was 86. Of the patients, 50% participated in strenuous/very strenuous activities, and kneeling pain was present in 63%. Radiographic degenerative change was found in 61%; 20% had IKDC grade C, and 0% had grade D. The IKDC clinical examination revealed that 95% had a normal/nearly normal knee. Significant sex differences existed: when compared with male patients, female patients were less likely to reinjure the reconstructed ACL (18% vs 2%, respectively; P = .01), reported poorer IKDC subjective scores (90 vs 83, respectively; P = .03), had more activity-related pain (20% vs 57%, respectively; P = .02), and were less likely to participate in strenuous activities (66% vs 35%, respectively; P = .009). ACL graft survival was not related to age. Patients <18 years old had an increased odds ratio (3.2) for rupturing the contralateral ACL. A coronal graft angle <17° increased the risk of failure compared with an angle >17° (77% vs 96% survival, respectively) by a factor of 8.5.

Conclusion:

Injuries more commonly occurred in the contralateral ACL than in the reconstructed ACL graft, and the most significant predictor of a contralateral ACL injury was age <18 years. The most significant predictor of an ACL graft rupture was a coronal graft angle <17°. Female patients had lower rerupture rates, poorer subjective scores, and decreased participation in strenuous activities, putting the graft at a lower risk of failure. Kneeling pain remained persistent over 20 years. Radiographic osteoarthritis was evident in 61% of patients, but symptomatic osteoarthritic symptoms were rarely reported.

Keywords

knee anterior cruciate ligament (ACL)reconstruction long-term outcome

Injuries to the anterior cruciate ligament (ACL) may lead to recurrent episodic instability, pain, meniscal injuries, osteoarthritis (OA), and poor quality of life and adversely affect long-term function of the knee.^{6,7,10,11,21,28,30,39} Endoscopic reconstruction aims to provide the patient with a stable knee by means of reproducing the anatomy of the ACL, thereby reducing the potential for adverse long-term intra-articular sequelae.²¹ Arthroscopic reconstruction is considered the gold standard for the treatment of ACL ruptures.^9,14,23,27 The literature suggests that there is not enough evidence to determine whether reconstruction of the ACL prevents arthritis in the long term.^13,16,21,29

Few studies have reported the long-term outcomes of single-incision endoscopic reconstruction of the ACL without associated other injuries including meniscal, collateral ligament, and chondral surface damage.^{6,22,27,37,38} This prospective study excludes these confounding factors and has been reported in the literature at 2, 5, 7, 10, and 15 years after surgery.^12,33-36 The purpose of this study was to report the 20-year outcomes of isolated ACL ruptures treated with endoscopic reconstruction using middle-third patellar tendon autografts.

Methods

Patient Selection

Between January 1993 and April 1994, a total of 333 consecutive patients underwent ACL reconstruction. All patients had an ACL rupture diagnosed on clinical examination and confirmed at arthroscopic surgery and wished to return to sports involving pivoting, cutting, or sidestepping, or they had repeated episodes of instability despite nonoperative treatment and appropriate rehabilitation. Exclusion criteria included any associated ligament injury requiring surgery, evidence of chondral damage or degeneration, previous meniscectomy or meniscal injury requiring more than one-third meniscectomy at the time of reconstruction, abnormal radiograph result, abnormal contralateral knee, patients seeking compensation for their injury, and patients who did not wish to participate in a research study. Therefore, the study group consisted of 90 patients with an essentially isolated ACL injury. Ethical approval was obtained from an independent ethics committee.

Surgical Technique

The operative technique was standardized in all patients and has previously been described in detail.⁴¹ The senior author (L.A.P.) performed all procedures. Examination under anesthesia confirmed anterolateral rotatory instability and positive Lachman test findings in all patients. With the patient under general anesthesia, a single dose of intravenous cephalosporin was administered. The limb was exsanguinated using an Esmarch bandage, and a high thigh tourniquet was used. Diagnostic arthroscopic surgery was performed first, using high anterolateral and low anteromedial portals. Suturing of appropriate meniscal lesions was carried out using an inside-out technique. A central-third patellar tendon autograft was harvested through two 2-cm longitudinal incisions at the distal aspect of the patella and just medial to the tibial tubercle. The femoral tunnel was positioned 5 mm anterior to the posterior capsule insertion and was drilled through the low anteromedial portal with the knee in maximum flexion. The tibial tunnel was positioned on the line between the anterior tibial spine and the anterior horn of the lateral meniscus, immediately anterior to the posterior cruciate ligament. The graft was fixed on the femoral side with a 7 × 25–mm round-headed cannulated interference (RCI) screw (Acufex; Smith & Nephew) through the low anteromedial portal and a 7 × 25–mm RCI screw on the tibial side. The osseous tunnels were drilled 1 mm less than the diameter of the graft. The mean diameter of the tunnel was 9.6 mm (range, 8-11 mm). Final tibial graft fixation was performed in full extension. Full hyperextension, a stable Lachman test, and the anterior drawer test were performed under anesthetic in all patients.

Postoperative Protocol

Patients were admitted to the hospital for a median of 2 nights (range, 1-5 nights). Immediate weightbearing with the aid of crutches was encouraged. The median time of crutch use was 10 days (range, 2-21 days). An accelerated rehabilitation program commenced on postoperative day 1 to reduce pain and swelling, with the goal of achieving full extension by 6 weeks. The rehabilitation program included closed chain exercises with an emphasis on proprioceptive training. At 6 weeks, patients began jogging in straight lines. From 12 weeks, general strengthening exercises were continued with agility work and sporting activities encouraged. Return to competitive sport involving jumping, pivoting, or sidestepping was not permitted until 6 to 9 months after surgery.

Clinical Assessment

Assessments were performed by independent physical therapists or researchers with extensive experience in knee assessments. The clinical assessment included range of motion (ROM), ligament stability, instrumented knee testing using the KT-1000 arthrometer (MEDmetric Corp) with the manual maximum test, and the International Knee Documentation Committee (IKDC) Knee Ligament Evaluation Form.^4,8 Ligament stability was measured by the Lachman and pivot-shift tests.²⁵ The Lachman test was graded as 0 (negative), 1 (1-5 mm laxity), 2 (6-10 mm laxity), or 3 (>10 mm laxity) and the pivot-shift test as 0 (negative), 1 (glide), 2 (clunk), or 3 (gross). The subjective assessment included the Lysholm knee score and IKDC subjective knee function score.^4,8 The single-legged hop test was used for the functional assessment. Evaluations were conducted preoperatively, annually for 5 years, and then at 7, 10, 15, and 20 years after surgery; these were side-by-side comparisons.

Radiographic Assessment

The radiographic examination was performed as a side-to-side comparison using bilateral weightbearing 35° to 45° posteroanterior, anteroposterior, lateral, and patellar skyline views. Radiographs were classified according to the IKDC guidelines as follows: A = normal, B = minimal changes and barely detectable joint space narrowing, C = moderate changes and joint space narrowing of up to 50%, and D = severe changes and >50% joint space narrowing. This grading has been shown to be both reliable and reproducible with longitudinal data.²⁵ An experienced musculoskeletal radiologist graded all radiographs. The tunnel position was assessed in the sagittal and coronal planes, and the graft inclination angle was measured using a method that has previously been described in detail.³⁵

Statistical Analysis

All data were assumed to be nonparametric. The Wilcoxon signed-rank test was used to assess change over time. Comparisons between subgroups were performed with the Mann-Whitney U test. Logistic regression analysis was used to assess the relative contribution of selected variables on dichotomous outcomes. Statistical significance was set at P = .05. SPSS 11.0 for Windows (SPSS Science Inc) was used for all the above statistical analyses. The outcomes were compared between sexes using the Mann-Whitney U test for continuous measurements (mean KT-1000 arthrometer, Lysholm score) and the χ² test for ordered categorical variables (IKDC categories, Lachman test, pivot-shift test). Logistic regression was used for the relationship between radiological outcomes and the variables of further surgery and tunnel placement. Survivorship of the ACL graft and contralateral ACL was calculated using the Kaplan-Meier survival method. Comparisons of survival curves were made with log-rank tests and univariate Cox regression. The influence of the factors of age <18 years, family history, sex, and graft angle on ACL graft survival was assessed as well as the influence of the factors of age <18 years and sex on contralateral ACL survival. Factors that were significant (P < .05) on univariate survival analysis were entered into multivariate Cox regression and then eliminated in a step-wise fashion until only the independent significant factors remained. Statistical significance was set at a 5% level.

Results

Study Group

A total of 90 patients met the inclusion criteria. There were 46 men (51%) and 44 women (49%). The left side was involved in 35 patients (39%) and the right in 55 (61%). The mean age at the time of reconstruction was 25 years (range, 15-42 years). Reconstruction was performed within 3 weeks of injury in 3 patients (3%), between 3 and 12 weeks in 64 (71%), and after 12 weeks in 23 (26%). All patients had a preoperative Lachman test result of grade 1 or 2, and 94% had a positive pivot shift; the remainder had locked knees, and a pivot shift could not be performed. Three patients (3%) with an acute injury had grade 2 laxity of the medial collateral ligament; all were successfully treated by a preoperative hinged ROM brace with an extension block at 30° for 6 weeks. Seventy-seven patients (86%) had intact menisci at the time of ACL reconstruction. Seven (8%) required meniscal sutures at the time of surgery, and 6 (7%) required excision of less than one-third of the meniscus.

Further ACL Injuries

Overall, 32 patients (36%) sustained a subsequent ACL injury, either an ACL graft rupture or contralateral ACL injury, at 20 years. Eight patients (9%) ruptured the ACL graft at a median of 82 months (range, 12-240 months) postoperatively. These patients subsequently underwent revision ACL reconstruction. An ACL graft rupture occurred in 7 male patients and 1 female patient.

There were 27 patients with a contralateral ACL rupture at a mean of 82 months postoperatively (range, 22-165 months). These patients were excluded from subsequent instrumented testing and single-legged hop test data, which assumes a normal contralateral knee. Of the 27 contralateral ACL ruptures, 25 underwent ACL reconstruction. There were significantly more contralateral ACL ruptures than graft ruptures over the 20-year follow-up period (P = .01). Three patients sustained both an ACL graft and contralateral ACL injury.

Complications

There was 1 superficial wound infection in the proximal wound of the graft harvest that was treated successfully with oral antibiotics. Two patients developed patellar tendinitis at 9 and 23 months postoperatively and were treated successfully with analgesia and physical therapy. Further surgery was needed in 37 patients. In 22 patients, surgery was performed on the contralateral knee; 13 patients had surgery to the reconstructed knee, and 6 required surgery to both the reconstructed and contralateral knees (Table 1). In total, there were 9 meniscectomies performed after ACL reconstruction over the 20-year period. All meniscal tears occurred during sporting activities. One patient died of unrelated causes at 9 years postoperatively. Contralateral meniscectomy was performed in 4 patients. These procedures occurred at 44, 72, 96, and 99 months in each patient, respectively.

Table 1

Further Surgeries Over 15 Years^a

	No. of Patients	Months Postoperatively
Surgery to index knee
Revision ACL reconstruction^b	6	12, 18, 76, 91, 126, 182
Partial meniscectomy	9	14, 18, 62, 69, 99, 99, 204, 220, 228
Arthroscopic debridement of cyclops lesion	2	6, 242
Arthroscopic arthrolysis	1	3
Excision of patellar tendon cyst	1	24
Arthroscopic chondroplasty	1	21
Removal of tibial screw	1	87
Surgery to contralateral knee
Contralateral ACL reconstruction^b	25	Mean, 82 (range, 22-165)
Contralateral partial meniscectomy	4	44, 72, 96, 99

ACL, anterior cruciate ligament.

Follow-up

The mean follow-up time was 245 months (range, 231-259 months). There were 80 patients reviewed at 20 years. Of the 10 patients not reviewed, 1 died of unrelated causes, 3 refused research participation, 2 were unable to be located, and 4 did not attend. The participant flow is shown in Figure 1.

Patients who sustained ruptures of the ACL graft were reviewed, and a summary of their results is shown in Table 2. Reviews were therefore performed on 72 of a possible 81 living patients with intact ACL grafts (89%) at 20 years.

Table 2

Results of the 8 Patients Who Had an ACL Graft Rupture^a

Results
Proceeded to revision ACL reconstruction	6/8 (75)
Effusion	1/6 (17)
IKDC score, mean (range)	84 (66-93)
IKDC ligament grade A	4/6 (67)
IKDC range of motion grade A	4/6 (67)
IKDC overall grade
A	2/6 (33)
B	2/6 (33)
C	2/6 (33)
IKDC radiological grade
A	2/7 (29)
B	2/7 (29)
C	3/7 (42)
D	0
Strenuous or very strenuous activities at 20 years	2/8 (25)

Results are reported as no. of patients/total assessed (%) unless otherwise indicated. All 8 patients completed subjective review, and 6 completed clinical review. ACL, anterior cruciate ligament; IKDC, International Knee Documentation Committee.

Self-reported Assessment

Lysholm Knee Score

The Lysholm knee score is designed to evaluate specific symptoms relating to knee function (limp, need for support, locking, instability, pain, swelling, and impairment of stair climbing or squatting ability). The best score is 100. The preoperative median Lysholm knee score was 64 (range, 6-97). At 20 years, the median Lysholm knee score was 95 (range, 55-100).

Subjective Knee Assessment (IKDC)

At 20 years after surgery, the mean subjective IKDC score at 20 years was 86 of a possible 100 (range, 28-100).

Activity

At 20 years after surgery, the mean age of the patients was 45 years. Regular participation was 35% (n = 25) in very strenuous activities such as soccer and basketball, 15% (n = 11) in strenuous activities such as skiing or tennis, 38% (n = 27) in moderate activities such as running or jogging, and 13% (n = 9) in light activities such as walking.

Symptoms With Activity

At 20 years after surgery, very strenuous or strenuous activities could be performed without pain in 78% (n = 56) of patients, without swelling in 76% (n = 55) of patients, and without giving way in 88% (n = 63) of patients.

Kneeling Pain

The proportion of patients with kneeling pain or difficulty is reported in Figure 2. There was a significant increase in the incidence of kneeling pain between 2 and 20 years (P = .001).

Sex Analysis

Female patients demonstrated a significantly lower incidence of ACL graft ruptures compared with male patients but also poorer subjective outcomes and lower reported activity levels, as shown in Table 3.

Table 3

Comparison of Outcomes for Female and Male Patients at 20 Years^a

	Female (n = 42)	Male (n = 38)	P Value
ACL graft rupture, %	2	16	.03
Contralateral ACL, %	26	35	.34
Subjective review, no. of patients	37	35
IKDC subjective score, mean ± SD	83 ± 16	90 ± 13	.03
Participating in strenuous or very strenuous activities at 20 years, %	35	66	.009
Pain with very strenuous activities at 20 years, %	57	20	.02
Objective review, no. of patients	22	22
IKDC ligament grade normal, %	96	68	.03
Overall IKDC grade normal, %	86	55	.05
Radiological grade normal, %	39	40	.31

ACL, anterior cruciate ligament; IKDC, International Knee Documentation Committee.

The proportion of male and female patients participating in strenuous activities at each review is shown in Figure 3. A greater proportion of male patients reported participating in strenuous sports at 2 years (P = .09), 15 years (P = .01), and 20 years (P = .009).

Male patients had a higher mean Lysholm score than female patients at 2 years (P = .05), 5 years (P = .06), 10 years (P = .09), 15 years (P = .008), and 20 years (P = .20) (Figure 4).

Clinical Assessment

The IKDC clinical assessment assumes a normal contralateral ACL. At 20 years after surgery, there were 57 living patients with an intact ACL graft and contralateral ACL eligible for 20-year review. A review was performed on 44 of 57 (77%) at 20 years. Of the 13 patients without clinical review, 6 had moved interstate or overseas and were unable to attend for geographical reasons but did complete subjective review, 3 refused ongoing participation in research, 2 did not attend, and 2 were unable to be located. The results are summarized in Table 4.

Table 4

Summary of IKDC Clinical Examination at 20 Years (n = 44)^a

	Grade A (Normal)	Grade B (Nearly Normal)	Grade C (Abnormal)
Effusion	40 (90)	4 (9)	0 (0)
Lachman test	37 (84)	7 (16)	0 (0)
Pivot-shift test	42 (95)	2 (5)	0 (0)
KT-1000 arthrometer	38 (86)	6 (14)	0 (0)
IKDC ligament	37 (84)	7 (16)	0 (0)
IKDC range of motion	38 (86)	4 (9)	2 (5)
IKDC overall	31 (70)	11 (25)	2 (5)
Single-legged hop test^b	35 (83)	7 (17)	0 (0)

Results are reported as n (%). IKDC, International Knee Documentation Committee.

Not performed by 2 patients.

Range of Motion

At 20 years after surgery, 39 of 44 patients had extension within 3° of the contralateral limb. There were 4 patients with 3° to 5° loss of extension, and 1 patient had 10° loss of extension. The patient with 10° extension loss was a 43-year-old male patient with IKDC grade C on radiographs and a subjective IKDC score of 89. Of the 44 patients, 43 had a flexion range within 5° of the contralateral limb, and 1 patient had 25° flexion loss. The patient with 25° flexion loss had a recent knee injury and magnetic resonance imaging and clinical findings consistent with a medial meniscal tear. The percentage of patients with extension loss increased significantly between 2 and 5 years (P = .002), but there was no change between 2 and 20 years (P = .46).

Single-Legged Hop Test

The single-legged hop test of knee function determines the percentage of the distance achieved by hopping on the involved limb compared with the contralateral normal limb. Two patients did not undergo the assessment because of a recent ankle or hip injury. Thirty-five patients (83%) were able to hop ≥90% of the contralateral limb, and 17% (n = 7) were able to hop between 76% and 89% of the contralateral limb.

Ligament Testing

Table 4 demonstrates the percentage of patients with normal (0- to 2-mm laxity) or nearly normal Lachman test (3- to 5-mm laxity), pivot-shift test, and instrumented testing findings at 20 years.

Overall IKDC Grading

Table 4 shows the 20-year IKDC grade for the 3 subgroups of effusion, ROM, and ligament evaluation and the overall IKDC grade. The overall IKDC score is a very conservative scale because the worst rating of any item in a given group determines the overall group rating. Therefore, only patients with a normal knee will be rated class A.²⁶

Radiographic Assessment

Radiographs were reviewed in 61 patients. The compartment with the most degenerative changes determines the overall IKDC radiographic grade. Results are shown in Figure 5 and Table 5. Overall, 61% had evidence of OA at 20 years after surgery. However, only 20% of patients showed grade C changes at 20 years, and there were no grade D findings.

Table 5

Summary of IKDC Radiographic Examination at 20 Years (n = 61)^a

	Grade A (Normal)	Grade B (Nearly Normal)	Grade C (Abnormal)
Medial tibiofemoral	29 (48)	23 (38)	9 (15)
Lateral tibiofemoral	51 (83)	9 (15)	1 (2)
Patellofemoral	42 (69)	11 (18)	8 (13)
Overall	24 (39)	25 (41)	12 (20)

Results are reported as n (%). IKDC, International Knee Documentation Committee.

Radiological Tunnel Placement

Of the 90 patients, 85 had a suitable postoperative radiograph available for the measurement of radiological tunnel placement using the previously described method²² (Table 6).

Table 6

Comparison of the Parameters of Tunnel Placement Between Patients With Ruptured Grafts and Those With Intact Grafts at 20 Years^a

	Intact ACL Graft (n = 78)	Ruptured ACL Graft (n = 7)	P Value
Tunnel placement, %
Sagittal femoral	85 ± 8	78 ± 10	.05
Sagittal tibial	41 ± 9	36 ± 5	.20
Coronal graft inclination, deg	19.7 ± 4	16.2 ± 4	.05

Values are reported as mean ± SD. ACL, anterior cruciate ligament.

Survival Analysis

ACL graft survival was 96%, 94%, 94%, and 90% at 5, 10, 15, and 20 years after ACL reconstruction, respectively (Figure 6). Survival of the contralateral ACL was 86%, 75%, 71%, and 67% at 5, 10, 15, and 20 years after ACL reconstruction, respectively (Figure 6).

If the coronal graft angle was <17°, the odds for an ACL graft rupture were increased by a factor of 8.5 compared with those with a coronal graft angle of ≥17° (95% CI, 2-47; P = .01) (Figure 7). The 20-year survival of the ACL graft was 96% in those with a graft angle of ≥17° and 77% in those with a graft angle of <17°. On multiple regression analysis, ACL graft survival was not significantly affected by the factor of age <18 years at the time of reconstruction (odds ratio [OR], 1.1; 95% CI, 0.1-9.8; P = .91), family history of ACL injury (OR, 2.0; 95% CI, 0.5-8.2; P = .35), or sex (OR, 7.1; 95% CI, 0.8-62; P = .08).

Regression analysis of contralateral ACL survival showed that patients <18 years old had a 3.2-times greater odds of a contralateral ACL rupture than those >18 years old (95% CI, 2.3-22.8; P = .001). The survival of the contralateral ACL was 44% in those aged <18 years compared with 75% in those aged ≥18 years (Figure 8). Contralateral ACL survival was not influenced by patient sex (OR, 1.1; 95% CI, 0.3-3.0; P = .92) or family history of ACL injury (OR, 1.1; 95% CI, 0.5-2.8; P = .79).

Discussion

This study reports the 20-year outcomes of endoscopic ACL reconstruction using middle-third patellar tendon autografts. It is known that other associated injuries in the knee (such as chondral damage) can result in a poor outcome despite ACL reconstruction. This study reported the findings of “isolated” ACL injuries requiring reconstruction based on the adopted exclusion criteria. It is, however, noted that it is difficult to achieve this in reality and that the truly “isolated” ACL probably does not occur. The strict inclusion criteria resulted in approximately 30% of patients with ACL ruptures over the study period being eligible for the study. Interpretation of the outcomes of this study cannot be generalized to the wider population of ACL-injured knees but rather represents the best-case scenario after ACL reconstruction.

Osteoarthritis

The long-term role of ACL reconstruction preventing OA has not been well established in the literature, but its role in meniscoprotective functioning preventing further damage to the menisci has been shown in several studies.^10,38 In this series, 9 patients required further meniscectomy, 6 of which were performed in the first 15 years after reconstruction and 3 meniscectomies were performed between the 15- and 20-year period. By comparison, 4 patients underwent meniscectomy in the contralateral knee. In a prospective study of nonoperatively treated ACLs, the incidence of meniscal surgery was 54% over 5 years and in other studies reported as high as 95% at 20 years after injury.^17,28 By comparison with the literature, our findings support the hypothesis that ACL reconstruction is effective in reducing further meniscal damage compared with nonoperative treatment.

Our results suggest that bone–patellar tendon–bone (BPTB) ACL reconstruction is not as arthrogenic, as previously suggested in the literature.^15,29 In this series, radiological degenerative change was present in 27% of patients at 5 years, 51% at 15 years, and 61% at 20 years. However, the proportion of patients with moderate to severe changes was low; only 20% of patients had grade C (up to 50% joint space narrowing) changes at 20 years, and there were no grade D changes. This is in contrast with other studies looking at the progression of OA in ACL-reconstructed knees, where higher levels of more severe degenerative changes are seen, with some as high as 20% at 10 years with moderate to severe radiographic changes.^1,15,29 The presence of other injuries in the knee such as chondral injuries or meniscal tears may increase the rate and degree of OA,^{11,20,21,28,31,32,39} and this may account for the lower incidence reported in our series compared with others. It should be remembered that the cohort of patients in this study would now be a mean age of 45 years. Others have shown that in the painful knee population, the incidence of radiographically detectable OA in the 35- to 54-year age group is 5%.³² BPTB ACL reconstruction does not appear to be associated with high rates of moderate to severe radiological degenerative change over 20 years, but it may be higher than the incidence seen in the general population, suggesting that this procedure does not prevent OA, but it may reduce the severity of premature degeneration when the meniscus is preserved.

Clinical Outcomes

Clinical outcomes revealed that 95% of patients with intact ACL grafts had a normal or nearly normal knee at 20 years according to IKDC criteria. High subjective scores were maintained over 20 years, and normal ligament examination findings were seen in 84%. With regard to ROM, only 1 patient had a loss of extension >5°, and there was no statistically significant progression of loss of extension between 2 and 20 years, which is consistent with previous studies.^23,24 At 20-year follow-up, 50% of patients were back to strenuous activities, which suggests that ACL reconstruction with BPTB is an effective procedure for getting patients back to sporting activity. Kneeling pain is a persistent issue after surgery, despite a 2-incision approach. It is important to document that this common postoperative finding persists in up to 67% at 20-year follow-up, so it must be addressed as part of the patients’ education on this procedure. ACL reconstruction with BPTB is a well-tolerated procedure with good clinical and subjective outcomes maintained over 20 years.

Sex-Based Differences

Female patients in this study demonstrated unfavorable outcomes compared with male patients with respect to a lower IKDC subjective score, were more likely to report pain on strenuous exercise, and were less likely to participate in strenuous activities. Female patients also had a lower incidence of ACL graft ruptures (2%) compared with male patients (16%) (P = .03), although patient sex did not achieve statistical significance on multiple regression analysis of ACL graft survival (P = .08). Poorer subjective outcomes seen in female patients compared with male patients may preclude activities at a strenuous level, thereby limiting the reconstructed ACL exposure to activities that could place the graft at risk of failure and result in a lower incidence of graft ruptures. ACL reconstruction with BPTB has a favorable outcome for female patients compared with male patients with regard to ACL graft ruptures but may be poorly tolerated with respect to subjective outcomes.

Further ACL Injuries

Contralateral knee ACL ruptures occurred more frequently than ACL graft ruptures. Survival of the contralateral ACL was 67% at 20 years compared with 90% in the reconstructed ACL. Previous studies have reported ACL rupture rates of BPTB of 6% to 13% between 10 and 15 years.^23,40 The higher incidence of contralateral ACL injuries compared with ACL graft ruptures could be caused by a number of factors, including the potential genetic and biomechanical considerations putting the native ACL at risk, the possibility of the patient favoring the reconstructed knee, or the fact that BPTB reconstruction is stronger than the native ligament.

Outcomes After ACL Graft Ruptures and Revision Surgery

Patients who had a BPTB graft rupture had a higher incidence of radiological degenerative changes (71%) compared with those with intact ACL grafts (60%); however, their mean IKDC subjective scores were still high at 20 years (mean, 84). The outcomes of failed BPTB reconstruction may be associated with a slightly higher incidence of degenerative changes but not necessarily poorer subjective outcomes.

Tunnel Placement

It has been documented that a common cause for failure of ACL reconstruction is suboptimal positioning of the bone tunnels in both the femur and tibia.³⁵ At 20 years, ACL graft survival was significantly lower in those with a coronal graft angle of <17°, with an 8.5-times greater OR compared with those with a graft angle of >17°. More vertical graft placement is associated with increased failure because of persistent anterolateral rotational instability.^2,19 Over recent years, there has been a trend toward placing the femoral tunnel lower on the lateral wall of the intercondylar notch.^5,18 The mean coronal graft angle was 19° in this series, which may be higher than current trends. Whether the current trend for lower placement of the femoral tunnel on the intercondylar notch results in lower rates of ACL graft ruptures is yet to be shown.

Age

When compared with patients older than 18 years, those younger than 18 years at the time of ACL reconstruction did not have higher rates of ACL graft ruptures but did have higher rates of contralateral ACL ruptures. More than half of those aged <18 years (56%) had a contralateral ACL rupture over 15 years. Other studies have shown that adolescents may well have a higher risk of ACL graft ruptures, have a higher preoperative activity level, have issues with compliance with rehabilitation, and be more likely to place the graft at risk.^3,26 Our study has not shown ACL graft survival to be significantly lower in adolescents than adults. However, the strongest predictor of contralateral ACL ruptures was age <18 years compared with age >18 years (56% vs 25%, respectively). This could be because of multifactorial aspects of this age group, including pre-existing genetic or biomechanical factors placing the native ACL at risk, that the BPTB graft is stronger than the native ACL. Patients may also favor the reconstructed knee, placing the contralateral knee at an increased risk of injury.

There are some limitations to this study. The strict inclusion criteria were designed to examine and report the natural history of ACL reconstruction without the confounding effects of other injuries. It must be noted that this represents approximately 1 in 3 of ACL-reconstructed patients, and the results of this study are not generalizable to those with confounding injuries, such as meniscal or cartilage damage, which is likely to worsen outcomes. The strengths of this study include the very high follow-up over 20 years, the prospective longitudinal deign, and the homogeneous group of patients who were treated by a single highly experienced knee surgeon, ensuring consistency in surgical technique. The arthroscopic surgical technique reported in this study is consistent with modern techniques, with femoral tunnel drilling via the anteromedial portal.

Conclusion

This study reports the long-term outcomes of patients having undergone middle-third BPTB reconstruction at 20 years. In the reconstructed knee, good long-term outcomes with regard to subjective scores and return to strenuous activities governed by a stable knee with good ROM are demonstrated. We have shown that female patients may have unfavorable outcomes with regard to subjective scores and pain, which may protect the ACL graft from further injuries. The radiological assessment of graft inclination angle is an important predictor of ACL graft ruptures, contralateral ACL injuries are common, especially in the young, and OA progression may not be as common as previously suspected.

Footnotes

One or more of the authors has declared the following potential conflict of interest or source of funding: Institutional research funds have been received by L.P. from Smith & Nephew in the past 5 years.

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