Though not fully investigated, there is increasing evidence that the level of activity to which an athlete returns after ACL reconstruction is a significant risk factor for graft failure. Those that return to higher levels of jumping, cutting, and start/stop activities are more likely to have a re-tear of their graft.

Borchers et al. demonstrated in a case-control study that higher activity level after reconstruction puts the patient at increased risk for graft failure [25]. This 1:2 case to control matched design identified 21 patients with ACL graft failures from the Multicenter Orthopedic Outcomes Network (MOON) prospective cohort database. MOON is a multicenter research consortium dedicated to studying clinical outcomes following ACL reconstruction. In this study, only one surgeon’s data was used to minimize potential confounders. The 21 case subjects were compared to 42 age- and sex-matched controls. All subjects underwent the same surgical technique, as well as identical postoperative rehabilitation and return-to-play guidelines. Activity level was measured using the Marx activity scale which is a validated instrument quantifying the amount of running, cutting, decelerating and pivoting an individual performs on a 0–16 scale with 16 being the highest level [32]. The mean Marx scores for both case and control subjects at the time of initial ACL injury was 16. The graft failure group had a mean Marx score of 16 at the time of re-tear which averaged 12 months after reconstruction. This was compared to a mean Marx score of only 12 for the control group, at the same mean postoperative time period of 12 months. Restated, both the re-tear group and control groups had Marx 16 activity levels when they tore their native ACL. The re-tear group returned to Marx 16 activity after their ACL reconstruction, whereas the age and sex matched controls only returned to Marx 12 activity levels. Logistic regression was used to evaluate this outcome variable. Those athletes who returned to an activity score greater than 12 had a 5.53 greater odds of ACL graft failure than did those who returned to activity scores of 12 or less (95 % CI 1.18–28.61; p = 0.009).

Salmon et al. examined the rates of contralateral ACL rupture and ACL graft failure after reconstruction using either hamstring or patellar tendons [8]. This case series also identified patient characteristics that would increase the risk of injury or re-injury including activity level. Six hundred seventy-five patients with single limb ACL reconstructions were interviewed by telephone 5 years after surgery. Activity level in the form of an International Knee Documentation Committee scale score was collected. Six hundred twelve patients were followed-up and 39 patients had sustained a graft failure (6 %), whereas 35 patients sustained contralateral ACL tears (6 %). Athletes that returned to level 1 or 2 sports involving jumping, pivoting, and side-stepping increased the odds of contralateral knee ACL tear by a factor of 10. With respect to the ACL reconstructed knee, 8 % of those that returned to level 1 or 2 sports had a re-tear compared to only 4 % of those that only returned to level 3 or 4 sports (adjusted OR = 2.1; 95 % CI 1.0–4.6; p = 0.05).

In a retrospective comparative study, Barrett et al. analyzed outcomes of bone-patellar tendon-bone (BT) fresh-frozen allograft ACL reconstructions in patients under the age of 40 with regard to Tegner activity scores [26]. Patients were required to have a minimum of 2 years of follow-up, no concomitant ligament injuries or prior surgeries. Seventy-eight of 111 patients met inclusion criteria and were available for follow-up. The control group consisted of 411 BTB autograft ACL reconstructions. Allograft reconstruction patients who returned to higher activity had a 2.6-fold increase of failure rate compared to low-activity allograft patients (p = 0.048).

Shelbourne et al. followed 1,820 patients prospectively for 5 years following primary ACL reconstruction using BTB autograft, and complete follow-up data was obtained on 78 % of patients (n = 1,415) [27]. Activity level data was collected including the time at which they returned to full activity, the type of activity, as well as the level to which they returned. This information was collected during office visits in the first year and yearly by mail subsequently. Jumping, twisting, pivoting sports at the collegiate or professional level were rated as 10, school-age or club level as 9, and recreational level as 8. They concluded that return to higher activity correlated with higher re-tear rates.

Laboute et al. in their analysis of 298 ACL reconstructions found the following re-tear rates by level of competition: regional 8.1 %, national 10.4 %, international 12.5 % [33]. Though this trend did not reach statistical significance, it is in keeping with the other studies demonstrating increasing level of activity as a risk factor for graft failure.

If returning to a higher level of activity after an ACL reconstruction increases one’s risk of graft re-tear, the next question that arises is whether the timing of return to full activity influences risk of re-tear. This issue has not been prospectively studied. The timing of return to full activity could be associated with the graft’s biologic incorporation as well as the patient’s recovery of neuromuscular control; both of which may be time dependant. Shelbourne et al. in their analysis of re-injury within 5 years after ACL reconstruction with patella tendon grafts found that return to full activity before or after 6 months did not significantly affect graft failure rates [27]. Tanaka et al. in their conclusions recommended that early return to activity should be avoided as all of their failures occurred early and none after 2 years [30]. Laboute et al. reported that athletes that returned to full activity prior to 7 months had a higher re-tear rate than those that returned at greater than 7 months: 15.3 % vs. 5.2 % (p = 0.0014) [33].

In summary, activity appears to be a significant risk factor for graft re-tears after ACL reconstruction. There are several quality studies that all indicate that returning to higher activity levels after reconstruction places the graft at a greater risk for re-tear. This intuitively is consistent with the observation that participation in aggressive deceleration and cutting sports places the native ACL at risk for failure. The timing of when patients return to full activity and its influence on ACL reconstruction outcomes warrants further study.

While native ACL injuries occur more often in women than men, there is conflicting evidence in the literature regarding whether gender is a significant risk factor for ACL graft failure. Wright et al. using the MOON prospective cohort, found a revision rate of 3 % (n = 7) of 235 subjects at a follow-up of 2 years [29]. Male patients constituted six of the seven failures. This did not however translate to a statistically significant difference given the sample size. Tanaka et al. found a rate of 9.4 % re-tears in a case series of 64 female basketball players [30]. Stevenson and Noojin have shown greater re-tear rates in females, but were not able to show statistical significance [9].

Shelbourne et al. showed no difference for re-tear between men and women (p = 0.5543) in their overall cohort [27]. However, boys did show a statistically higher graft failure rate in the group of patients <18 years of age.

Salmon et al. also showed a higher percentage of males experiencing re-tears than women at overall incidence rates of 8 % (30/383) and 4 % (9/229), respectively; however, this did not reach statistical significance (95 % CI 0.4–1.9; p = 0.67) [8]. Barrett et al. did not find sex as a significant risk factor for re-tear in their analysis of 263 males and 226 females [26]. The studies by Kaeding et al. [31] and Laboute et al. [33] also did not find a difference in graft re-tear rates between males and females.

The above studies did not do an adequate job at controlling for return to activity after ACL reconstruction. If there is a difference in the post-reconstruction activity level between the male and female groups then no meaningful comparison can be made.

Paterno et al. performed a systematic review comparing sex differences in ACLR outcomes by graft type [34]. One factor that may contribute to AP knee laxity after ACLR is the strength and integrity of the graft type used to reconstruct the native ACL. The debate on optimal graft type choice for ACLR remains controversial. The two most commonly used autogenous grafts include the BTB and hamstrings tendon (HS) [1, 35, 36]. Advantages of BTB grafts include tissue accessibility for graft harvest, strong structural properties, bony fixation (potential for bone-to-bone healing) and predictable success rate in restoration of knee stability [37]. On the contrary, advantages of HS grafts include fewer donor-site complications [37]. Reconstructions with HS grafts tend to demonstrate increased anterior laxity with time post surgery [38–40]. Many authors continue to recommend HS grafts as a viable, stable alternative to BTB grafts, and there has been a large increase in the relative percentage of HS grafts used by sports medicine surgeons in the United States and abroad [41, 42].

Sex differences in AP knee laxity between HS and BTB grafts have been reported by multiple studies. In general, females with a HS graft have demonstrated significantly greater AP knee laxity than males with a HS graft [3–5, 41]. Muneta et al. reported that patients who received a HS graft had a greater percentage of subjects with greater than 5 mm of asymmetry in AP knee laxity [6]. In addition, there were more females with greater than 5 mm of asymmetry in AP knee laxity than males. Pinczewski et al. reported that females with a HS graft ACLR had significantly greater AP translation and significantly fewer patients with less than 3 mm of asymmetry than males with an identical procedure at 2 years post-reconstruction [7]. The change in their outcome at 10 years when compared to 2 years postoperative may be related to subject drop out due to re-injury and contralateral injury. In addition to the studies that examined subjects with both HS and BTB grafts, studies that investigated only subjects with HS grafts presented similar results. Salmon et al. [43] and Noojin et al. [9] noted greater AP translation in females when compared to males with HS grafts.

No studies that investigated the influence of sex and graft source on outcomes after ACLR reported significant sex differences in asymmetry in AP knee laxity with a BTB graft [34]. Ferrari et al. reported the mean side-to-side differences in AP knee laxity of male patients who had ACLR with a BTB graft was significantly less than in females [44]. However, there was no difference in the percentage of patients who had greater than 5 mm of asymmetry in AP laxity. The studies of stronger methodological design reported no significant difference in AP knee laxity between sexes following ACLR with a BTB graft. These results are consistent with other studies in the literature that reported no sex differences in AP knee laxity [45, 46] or graft failure [47, 48] with a BTB graft.

Females with a HS graft may demonstrate significantly greater side-to-side differences in AP translation than a cohort of females patients with a BTB graft [3, 5, 41]. Other studies also reported greater values in mean AP knee laxity asymmetries in females with a HS graft when compared to a BTB graft ACLR [3, 4]. Pinczewski et al. reported in a study with 10-year follow-up that there was no difference in mean AP laxity between the HS and BTB groups [7]. Taken together, these findings indicate that females experience greater asymmetry in AP knee laxity after an ACLR with a HS graft than with a BTB graft.

In summary, the evidence for sex as a risk factor for graft re-tear after ACL reconstruction is conflicting. This may be due largely to confounding factors such as activity level after ACL reconstruction. It is clear that for equal exposure to high risk sports, females have a 2–6 times increased risk of tearing their native ACL than males. If there is no difference between male and female re-tear rates after ACL reconstruction, then something has changed from the baseline conditions. Several scenarios can potentially explain this. One can speculate that the ACL graft is stronger than the native female ACL and that they are not at an increased risk after reconstruction compared to males receiving similar strength grafts. This would be supported by Shelbourne’s observation that females do not have an increased risk of tearing their ACL grafts, but do have an increased risk of tearing their contralateral native ACL compared to males [27]. This would assume that both lower extremities return to equal neuromuscular function, use and risk exposure. Another scenario would be that females continue to have their baseline increased risk of ACL injury after reconstruction but this is not observed because they do not return to as high a level of activity after reconstruction compared to males. This decreased exposure would hide their increased intrinsic risk. A third scenario would be that a neuromuscular adaptation is made during the surgery/rehabilitation process that reduces their risk.

Kaeding et al. demonstrated that age was a significant risk factor for graft failure using the MOON prospective longitudinal cohort. [31

Stay updated, free articles. Join our Telegram channel

Join