Introduction
Anterior cruciate ligament (ACL) rupture is a disabling knee injury which frequently occurs in young athletes. Previous studies have critically assessed risk factors for primary ACL injury, including variables such as gender, levels of sports activity, and anatomical characteristics [
1,
2]. Female to male ratio of ACL injuries in basketball players was 3.6 and 4.5 in high school and in college, respectively [
3].
ACL reconstruction is currently the gold standard to restore knee function after ACL rupture [
4], but long-term efficacy has not been fully established [
5]. ACL reconstruction using hamstring tendons has become a popular procedure because of its lower risk of donor site morbidity [
6‐
8]. In addition, recent improvement in operative procedures has made it possible to perform anatomical double-bundle ACL reconstruction. This offers several advantages over the traditional Rosenberg's one or two femoral sockets ("bi-socket") procedure, including better biomechanical outcomes and more favorable clinical results [
9‐
11].
However, with the increasing number of ACL reconstructions, graft failures have become more frequent. Rate of graft failures is reported as high as 8% of primary ACL reconstructions [
12], and causes for failures can be classified into three categories: technical errors, biological failures, and traumatic failures. However, risk factors of graft retears remain unknown [
13,
14], and a single study has examined the risk factors for ACL graft retears [
15]. The authors described the return to competitive sports as requiring movements such as side-stepping, pivoting, and jumping, and playing basketball was one risk factor for repeated ACL injury. Despite these facts, most athletes hope to return to sports activity following ACL reconstruction. The present study aimed to examine the incidence of ACL graft retear in female basketball players.
Discussion
Our case series revealed an ACL graft retear rate in female basketball players of 9.4%. Some studies which reported results from patellar tendon and hamstring reconstruction also described incidence of hamstring ACL graft retear, but did not necessarily focus on graft ruptures [
15,
19‐
22]. According to these reports, the retear rate ranged from 2% to 8%. Salmon
et al. concluded that risk factors of graft retear included return to competitive sports that require side-stepping, pivoting or jumping [
15]. Their findings are consistent with our data with regard to the high incidence of retear in female basketball players.
Previous reports describe external and internal risk factors of primary ACL injury in female athletes [
1,
2]. External factors include the type of competition, shoe-surface interface, and muscle strength. Internal factors include anatomical, hormonal, and neuromuscular risk factors. However, risk factors of ACL graft retears remain unknown.
Salmon
et al. reported incidence and risk factors of ACL graft rupture and contralateral ACL rupture over five years after reconstruction [
15]. Repeated ACL injury occurred in 12% of the patients, and risk factors included a return to competitive sports that require side-stepping, pivoting, or jumping, as well as the contact mechanism of the index injury. Rate of graft ruptures and contralateral ACL ruptures were both 6%, although graft ruptures occurred significantly earlier than did contralateral ACL ruptures. According to their data, approximately 70% of all ACL graft ruptures occurred postoperatively, within a 24-month period [
15]. Our data show that all graft retears were observed within the first 18 months. Furthermore, mechanisms of graft retear were completely different from those of the primary injury. While routine physical examination before re-injury revealed no instability in patients in the retear group, the remodeling phase of transplanted grafts is likely to continue throughout this period, and failures in graft maturation may influence retears. Based on these results, we would not recommend an early return to playing basketball.
Mean preoperative period of the retear group was shorter than that of the uninjured group, but the difference was not statistically significant. While we lack scientific evidence to support this, it is possible that a short preoperative duration might influence player condition. First, this could lower the likelihood that they will restore their physical condition including muscle strength, balance, and agility before ACL reconstruction. Second, it may influence their sense of fear. A long preoperative period seems to induce a sense of fear towards returning to their previous sports activity. However, in the absence of fear, patients do not hesitate to return to their sport after ACL reconstruction. As such, a shorter preoperative period may lead to ACL graft retear.
Mean age of the players was lower in the retear group than that in the uninjured group, but the difference was not statistically significant. However, all graft retears occurred in high school players. As young players are not supervised by an athletic trainer in most high schools, surgeons and physical therapists should provide stringent follow-up following ACL reconstruction.
Interestingly, preoperative quadriceps strength in the injured graft group was significantly lower than that in the uninjured group. A study by de Jong
et al. revealed an association between preoperative quadriceps strength and postoperative functional performance [
22]. The authors showed that an increased preoperative quadriceps deficit resulted in a lower postoperative function at six and nine months. In addition, they observed a quadriceps strength deficit of almost 20%, which persisted for one year. Residual quadricep weakness after ACL reconstruction has been shown in several studies [
23‐
27]. Measured with a Cybex dynamometer, Keays
et al. reported a 12% quadriceps strength deficit at 60° per second and a 10% deficit at 120° per second at six months [
26]. Kobayashi
et al. showed an approximate 10% quadriceps deficit postoperatively even after two years [
25]. Furthermore, many reports on chronic ACL-deficiency cases found an association between postoperative quadriceps deficit and functional performance [
23,
27‐
29]. However, our case series found no significant difference in postoperative muscle strength between the uninjured and injured groups. Accurate clinical relevance of preoperative quadriceps deficit in ACL graft retears remains unclear at the present time.
We hypothesize that patients who showed strength deficits might have deficits in agility, balance, and proprioception. Rendstrom
et al. noted that prevention of primary ACL injuries required a program which includes muscle strength and power exercises, neuromuscular training, and plyometrics and agility training [
2]. When deficits in these elements were retained postoperatively, patients returned to basketball not fully healed and in unsafe conditions. Further studies are required to clarify if preoperative muscle weakness reflects deficits in other elements.
Limitations of this study include the lack of functional assessment, the relatively short duration of follow-up, and the small number of retear cases. We recognize the importance of functional assessment, as well as evaluation of muscle strength in patients prior to returning to sports activity. As data were incomplete in most patients, we excluded results of the functional tests from the present study. Regarding follow-up duration, further observation is required to demonstrate long-term results of ACL reconstruction. However, our data in the present study demonstrated that re-injury occurred within 18 months after the index surgery, representing the reality of ACL graft retears. Further cases are required to clarify the validity of the present study results.
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
YT drafted the manuscript. SH and YY contributed to study design and manuscript structure. TK, NS and ST contributed to muscle strength assessment. YS advised clinical opinions for assessing retear cases.
All authors have read and approved the final manuscript.