Preoperative: Graft Selection (Autograft vs. Allograft, Graft Choice)

Bone-Patellar Tendon-Bone

Considered the “gold standard” by many surgeons, the bone-patellar tendon-bone (BPTB) autograft is the most commonly employed graft for ACL reconstruction. This autograft is harvested from the middle third of the patient’s patellar tendon and typically includes small bone blocks from the patella and the proximal tibia. Although many alternatives have been proposed, the BPTB graft is typically secured in the tibia and femur with metal or bioabsorbable interference screws that securely fixate the bone plugs within the tunnels. In addition to its high ultimate load-to-failure ratio in comparison with the native ACL (2977 N vs. 2100 N), the BPTB autograft has the advantage of osseous integration because of the presence of the bone plugs secured within the femoral and tibial tunnels, which allows for rigid fixation. ^, The BPTB autograft can be harvested from either the injured knee (the more common source) or, in some cases, from the contralateral knee. Freedman’s metaanalysis comparing BPTB and HT autografts demonstrated less residual anterior knee laxity in the reconstructions performed using the BPTB graft, as shown by the percentage of patients with less than 3 mm side-to-side differences in KT-1000 arthrometry testing. As such, the biomechanical stiffness of this graft makes it the most commonly used option for athletes.

However, several reported postoperative complications are important to consider in counseling patients on the selection of a BPTB graft. Kneeling pain is defined as pain produced by direct pressure on the patellar tendon. This symptom has been studied independently of generalized anterior knee pain and is detected by having the patient walk on his or her knees. Ejerhed reported kneeling pain in nearly twice as many patients who underwent ACL reconstruction with BPTB graft compared with HT autograft (53% vs. 23%). Anterior knee pain following patellar tendon harvesting is the most common postoperative complication, and occurs in up to 46% of patients. Interestingly, Shelton’s comparative study of autograft BPTB versus allograft BPTB ACL reconstructions demonstrated no difference in the incidence of anterior knee pain between the two cohorts at 15-month follow-up. Geib found the incidence of anterior knee pain to be more than 5-fold higher with BPTB autograft versus QT autograft with a single bone plug (27% vs. 5%). Most studies show a tendency for decreased knee pain with the use of HT autograft compared with BPTB as well. ^,

Because the knee extensor mechanism is disrupted with BPTB autograft harvest, loss of knee extension strength has been shown to be significantly greater in patients following use of a BPTB graft, with reported deficits of 20% at 1-year follow-up and 15% at 3 years. Patella fracture and anterior knee paresthesias are other potential donor-site complications, and are discussed in a later section.

The development of osteoarthritis following ACL injury and subsequent reconstruction, although multifactorial in nature, is a known sequela with a prevalence of 21% to 48% in patients with concomitant meniscal injury. A long-term prospective follow-up study by Pinczewski et al. demonstrated a significantly higher rate of radiographically evident osteoarthritis following ACL reconstruction in patients who had a BPTB autograft in comparison with HT autograft (39% at 10 years for BPTB compared with 18% at 10 years for HT). The reason for this increased rate of arthritis is unknown.

Despite these complications and its relative contraindications in patients with preexisting anterior knee pain or work-related kneeling requirements (such as priests, builders, plumbers, mechanics, and combat soldiers), the BPTB autograft remains the second most popular graft option for ACL reconstructions worldwide.

Hamstring

The use of the patient’s tendons for a graft source, specifically the semitendinosus alone or in combination with the gracilis, has been coined the HT autograft . Paradoxically, the gracilis is not a hamstring but an adductor. Like the BPTB, the ultimate tensile load of a quadrupled HT autograft (2352 N) is greater than that of the native ACL. The autograft can be harvested from the injured knee or from the contralateral limb. The tendons are typically identified at their insertion of the proximal tibia and then “stripped” from their muscle attachment. They are then typically prepared by folding the long tendons in half, resulting in a four-stranded graft of 7 to 10 mm in diameter. A major advantage of the HT autograft is the preservation of the extensor mechanism, the primary focus of postoperative rehabilitation following ACL reconstruction. When compared with the nonoperated leg, HT autograft has been shown in a level 1 study to provide higher maintained knee extension strength than BPTB (92% vs. 85%). As alluded to previously, this graft option is preferable when anterior knee pain is preexisting or mitigation of the risk is desired.

As expected, multiple studies have demonstrated that, following an ACL reconstruction using a HT autograft, patients have significantly lower knee flexion strength in the operated compared with the nonoperated leg in the immediate postoperative period than those who received a BPTB autograft (90% in HT autograft vs. 102% in BPTB autograft). ^, Level 1 evidence has shown however, that flexion strength deficits may be transient, and may not affect an individual’s level of participation in sporting activities at long-term follow-up. ^, An additional theoretical disadvantage of HT graft is the longer graft integration and healing times within bone tunnels owing to the absence of bone plugs because it has been shown in a canine model to take 12 weeks for collagen fibers to form an attachment to bone that resembles Sharpey’s fibers. The clinical significance of this prolonged ligamentization process remains uncertain. Another complication associated with HT autograft is the inconsistency of HT size. Smaller tendons will result in a smaller autograft diameter and may lead to increased failure. A case-control study of 491 primary HT autograft ACL reconstructions over a 6-year period with 1.9-year follow-up found a 0.82 times lower likelihood of a patient undergoing revision surgery with every 0.5-mm incremental increase in graft diameter within the range of 7.0 to 9.0 mm. In this cohort, a patient with a graft 9 mm in diameter was 55% less likely to have undergone a revision for graft failure than a patient with a graft 7 mm diameter. Although researchers have tried to predict tendon size with preoperative imaging, it remains a challenge to accurately identify patients with smaller tendons.

Quadriceps

A strip of QT with or without a bone block from the patella is a less commonly employed autograft source. Like BPTB autografts, QT autografts offer a high ultimate tensile load (2,352 N), as well as bone-to-bone healing when a patellar plug is harvested. Other added advantages over BPTB include reduced anterior knee pain (8.3% vs. 39%) and reduced incidence of paresthesia from cutting the infrapatellar branch of the saphenous nerve. The ability to customize graft length may be another benefit in patients where a short or long BPTB graft presents a length-tunnel mismatch. Lee reviewed 247 patients and found similar range of motion and International Knee Documentation Committee (IKDC) scores at 2-year follow-up in comparison with BPTB autografts.

However, similar to BPTB, loss of knee extension strength was reported to be 20% at 1 year. Additional disadvantages include cosmetic concerns and a more technically demanding harvest. A cadaveric study demonstrated an average postharvest QT strength of 2430 N following removal of a 10-mm wide strip of autograft tendon, which remains higher than that of a native patellar tendon. This may explain why residual quadriceps rupture is an uncommon cause of extensor mechanism disruption following ACL reconstruction. However, a single report of late donor site rupture at the vastus medialis has been reported in the literature in a patient whose knee buckled after missing three steps descending from a train ladder.