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Synopsis: Quadruple hamstring ACL reconstruction resulted in a 23% failure rate for female patients vs. a 4% failure rate for male patients.
Source: Noojin FK, et al. Clinical comparison of intraarticular anterior cruciate ligament reconstruction using autogenous semitendinosus and gracilis tendons in men versus women. Am J Sports Med 2000;28(6):783-789.
Hamstring ACL grafts have been increasingly popular because of the more cosmetically appealing incision and also the decreased morbidity from graft harvest. In addition, patients who have pre-existing patellofemoral pain may benefit from a graft choice other than bone patella tendon bone. This study by Noojin and colleagues critically looks at whether there are differences in males vs. females for outcomes following ACL reconstruction with hamstring autografts. Over a six-year period, a single surgeon performed 130 ACL reconstructions using hamstring grafts, corresponding to about 20% of the ACLs he performed. A single incision technique was used with femoral fixation using the endobutton. Tibial fixation was performed with either sutures tied around a post with a spiked washer, or sutures tied over a button. Demographics, meniscal tears, and chondral pathology were similar between groups.
At an average follow-up of almost 3½ years, patients were evaluated by physical examination, KT1000 arthrometry, visual analogue scale, and with Tegner and Lysholm scores for activity level and subjective outcomes. There was a significant difference in the clinical failure rate with nine out of 39 (23%) female patients failing vs. just one out of 26 (4%) male patients suffering clinical graft failure. In addition, there was also a trend toward increased laxity in the female patients by KT1000 testing, with a mean side to side difference of 1.8 mm vs. 1.25 mm in the males. Furthermore, 21% of the females had a side-to-side difference greater than 3 mm vs. 12% of the male patients. The female patients tended to have a bit higher Tegner score indicating an increased activity level, but this did not reach significance. Interestingly, seven of the nine failures in the female patients occurred with button fixation on the tibia as opposed to the screw and washer construct.
Other studies have been performed that have documented a difference in injury incidence for the ACL in female patients. Theories have included hormonal changes affecting ligament laxity and stiffness, as well as anatomical differences in the size of the femoral notch and the diameter of the ligament. Also, neuromuscular differences have been postulated that may be amenable to changing with plyometric training techniques. This is the first paper that documents a difference in outcomes after reconstruction based on sex.
The strengths of this paper include that it involved a single surgeon and a minimum of two-year follow-up, and that the patients were objectively evaluated with KT1000 arthrometry as well as by clinical examination with well-validated scoring systems. Weaknesses include the tibial fixation methods that are somewhat outdated for hamstring autografts. Currently, most people use a combination of double fixation both within the tunnel as well as outside the tunnel on the tibial side to improve stiffness and pull-out strength. Fixation outside the tunnel at both ends of the graft has been noted to increase the risk of bungie cord effect or creep, possibly causing lengthening of the graft as well as a windshield wiper effect and tunnel widening. That being said, we are still left with the difference between the two groups based on sex. None of these theories explain why the males had tighter knees with fewer graft failures than the females. It is possible that females had a smaller hamstring graft diameter placed in tunnels that were otherwise drilled to the same size, coupled with differences in bone density. Slightly increased generalized ligamentous laxity that has been noted in females vs. males may have also contributed, as well as neuromuscular differences or hormonal factors. We are still left with the failure rates that are quite different, and additional study will be needed on this very important topic.