Introduction

Anterior cruciate ligament (ACL) reconstruction has become one of the most commonly performed orthopaedic procedures. Multiple different graft choices are available to the treating surgeon for primary ACL reconstruction, including bone-patellar tendon-bone (BPTB), hamstring tendon (HT), or quadriceps autograft and multiple different allograft choices, including BPTB, HT, Achilles, tibialis anterior, and others. In recent years, the most commonly used graft choices have changed dramatically, from a predominance of BPTB, to a predominance of HT in some areas of the world, and finally the growth of allograft tissue use.

Multiple different factors are at play when choosing a graft for ACL reconstruction. These include graft strength, graft fixation, ability to heal in the bony ACL tunnels, tolerance to desired rehabilitation and return to sport, and long-term durability. However, in addition to survivorship, the treating surgeon must also take into account potential complications and associated graft-specific morbidity. Although these factors have been studied extensively, the respective weight that each treating surgeon applies to the individual factors in the graft choice decision is widely variable. Furthermore, an examination of the available literature results in multiple reports both for and against each graft choice. Consequently, each surgeon must critically evaluate which factors are the most important to their graft choice decision.

In this chapter, we present the case for BPTB grafts in ACL reconstruction. This presentation will include the rationale for our ACL graft choice as well as multiple literature references to support it. We will highlight the advantages of the BPTB graft for ACL reconstruction, as well as potential disadvantages of other graft choices. Also included is a review of multiple comparative studies pertaining to ACL graft choices. It is our hope that, upon completion of this chapter, we will present a concise case for why we utilize BPTB grafts in all ACL reconstructions.

The Ideal Anterior Cruciate Ligament Graft

Prior to evaluating individual grafts, it is important to first ponder the characteristics of an ideal ACL graft. An ideal graft would possess the perfect traits at each point from initial implantation, through rehabilitation and return to sport, and on to long-term function. The ideal graft would be a perfect biological match to the recipient. It would possess the biomechanical strength necessary to withstand normal function. It would be able to achieve easy fixation after implantation. The ideal graft would heal quickly and achieve biologic fixation and would tolerate aggressive rehabilitation without restriction. It would also allow for a full return to sports with long-term durability. Finally, it would be without donor site morbidity or graft-specific complications. Given these traits of an ideal ACL graft, we must evaluate each potential graft choice along these perfect criteria.

The Ideal Anterior Cruciate Ligament Graft

Prior to evaluating individual grafts, it is important to first ponder the characteristics of an ideal ACL graft. An ideal graft would possess the perfect traits at each point from initial implantation, through rehabilitation and return to sport, and on to long-term function. The ideal graft would be a perfect biological match to the recipient. It would possess the biomechanical strength necessary to withstand normal function. It would be able to achieve easy fixation after implantation. The ideal graft would heal quickly and achieve biologic fixation and would tolerate aggressive rehabilitation without restriction. It would also allow for a full return to sports with long-term durability. Finally, it would be without donor site morbidity or graft-specific complications. Given these traits of an ideal ACL graft, we must evaluate each potential graft choice along these perfect criteria.

Biologic Compatibility and Incorporation

ACL graft choices differ with regard to their biologic compatibility with the recipient. Obviously, autograft tissue, whether it is BPTB or HT, has the advantage of being an exact DNA match, which generates no immunologic response and carries low risk of infection. Allograft tissue, in addition to being nonviable at the moment of implantation, is not a DNA match, and introduces the potential for disease transmission and infection. A Centers for Disease Control and Prevention report on allografts in 2002 reported on 18 infections in ACL reconstructed with allograft tissue, most of which were spore-forming Clostridium species, including one death. While improvements in graft sterilization and preparation have improved since that time, the risk of viral or bacterial infection persists with allograft tissue.

Graft incorporation is likely slower when using allograft tissue as well. Muramatsu et al. showed with contrast-enhanced magnetic resonance imaging that revascularization of bone-tendon-bone allografts were significantly slower than autograft tissue. In this study the ACL allograft took between 12 and 24 months to revascularize and mature similar to the autograft. Conversely, Papageorgiou et al. studied a goat model with bone-tendon-bone autograft and found evidence of dense fibrous tissue surrounding the ACL bone plugs with near full incorporation at 6 weeks postimplantation. Furthermore, animal models have shown superior incorporation and graft strength with autografts compared with allograft.

Graft Strength

Graft tissue used for ACL reconstruction should ideally be as strong, if not stronger, than the native ACL. Biomechanical studies have shown the loading strength of different ACL graft types. The load to failure of the native ACL has been reported to be 2160N, with stiffness 242 N/mm. Cooper found that a 10-mm BPTB graft load to failure exceeded that of the normal ACL, with a mean value of 2977N. Wilson et al. reported no differences in graft stiffness between BPTB and hamstrings. However, clinically, stability results after ACL reconstructions have been shown to be similar or improved with BPTB versus HT. Although in the laboratory the quadrupled HT may be stronger and stiffer than BPTB, the biomechanical performance of the HT has not been shown to result in better stability outcomes or improved survivorship. On the contrary, multiple recent registry studies have shown increased revision rates with HS versus BPTB.

Furthermore, HT graft size varies from person to person. ACL reconstruction with a HT graft that is small in size and diameter leads to increased risk of failure. Mariscalco et al. reported a failure rate of 7% at just 2 years after ACL surgery with a HT graft less than 8 mm. However, the extensor mechanism is able to accommodate a 10-mm central graft in all cases, given its stout supporting retinacular structures to reinforce the remaining tendon. For this reason, BPTB is, in our opinion, preferred, given its reproducible graft size, regardless of patient and tendon size, and strong clinical performance.

Graft Fixation and Healing

BPTB grafts are superior to other graft options with regard to early graft fixation and healing due to the presence of bone plugs at each end. This allows the graft to have a customizable good fit within the ACL graft tunnels for either interference screw or suspensory fixation ( Fig. 15.1 ). Soft tissue grafts such as HT or quadriceps tendon without a bone block rely on interference screw or suspensory fixation of soft tissue being pressed against bone. Animal models have shown that this leads to a predictable healing phase that takes as much as 12 weeks to be biomechanically equivalent to BPTB grafts. The presence of bone plugs at the end of a BPTB graft allows for early biologic graft incorporation and healing in as little as 6 weeks from implantation. This is superior to soft tissue-to-bone healing with HT and quadriceps tendon grafts. As stated previously, allograft tissue has a far longer time for incorporation and healing. It seems clear that BPTB grafts are able to achieve superior initial fixation and early healing compared with soft tissue grafts or allografts.

The posteroanterior ( A ) and lateral ( B ) view radiographs show healed bone plugs in the tunnels with the use of button fixation.

Rehabilitation and Return to Sport

While much focus is given to surgical characteristics of each graft type, the implications that each graft type places on postoperative rehabilitation is equally important. Both the surgeon and the treating physical therapist must balance early aggressive rehabilitation methods versus the initial graft fixation in order to safely guard against early graft failure, but also encourage early return of function.

BPTB autograft reconstructions allow the most aggressive early rehabilitation strategies. While some protocols advocate brace immobilization in the early perioperative period, many centers do not. In our center, braces are not used at any time following BPTB ACL reconstructions. Our technique utilizes suture fixation over plastic buttons as previously described. Nonetheless, our early postoperative protocol stresses immediate range of motion (ROM) exercises, including full hyperextension symmetric to the opposite side, on the day of surgery. Furthermore, full weight bearing is allowed for ambulation. However, even with the supposed weak initial fixation of sutures over plastic buttons and aggressive rehabilitation, early graft failures do not occur. Given this information, our data has shown that with BPTB autografts, immediate full ROM and weight bearing is not only allowed, but is paramount to maximizing patient outcomes. Initiation of this aggressive rehabilitation protocol has made ROM problems rare, without any early graft failure.

HT grafts, however, are often not treated in this way. Rehabilitation programs for ACL reconstructions done with HT grafts routinely utilize brace immobilization, with specific restriction of hyperextension, in the early postoperative phase. Given the soft-tissue-to-bone healing process, more time must pass before biologic incorporation is reliable; thus more time must pass before return to sport is safe. Although many authors report return to sports with BPTB grafts of 6 months or less, some authors advocate a slower return to sports participation when a HS graft is used. This early ROM restriction and slower return to sports is unnecessary with a BPTB graft.

Patients with allograft reconstructions often are restricted from early return to sports as well. While the purported advantage of allografts is the avoidance of perioperative morbidity, this does not lead to a functional return to high-level sports at a faster rate. This is due to the relatively slower incorporation of allograft tissue to the host recipient. While BPTB grafts can heal to native bone in as little as 6 weeks, allograft healing is much slower, with full incorporation taking up to 12–18 months. Consequently, the optimal time for return to sports is uncertain, as the treating surgeon and therapist do not have good evaluation methods to assess graft strength and healing. Consequently, there is worry about reinjury rate with allograft reconstruction in high-level athletes; this worry has been validated by multiple studies revealing higher rates of graft re-rupture than BPTB.

Graft-Specific Complications

While each graft choice can boast its specific advantages, there are unquestionably complications that each must face. BPTB graft harvest from the extensor mechanism leaves weak points that are vulnerable to traumatic injury. Specifically, patella fractures and patella tendon ruptures can occur and may require operative fixation/repair for extensor mechanism discontinuity. Though less common, tibia fractures have been reported as well. Fortunately, these complications are rare. Plus, BPTB graft harvest can leave the patient with quadriceps weakness, anterior knee pain, anterior knee numbness and sensitivity, and difficulty with kneeling. Mastrokalos et al. reported their experience with contralateral patella tendon harvest and reported many of these complications to be common. While these may be due, in part, to the patella tendon graft, the causes are likely multifactorial. Shelbourne and Trumper, however, reported postoperative ACL scores that were nearly identical to knees with no injury and suggested that anterior knee pain may be due to inadequate ACL rehabilitation and persistent stiffness.

HT graft harvest can also have specific complications. Inadvertent truncation of the hamstrings during harvest can leave the surgeon with insufficient graft material. Furthermore, as noted previously, HT can be of small diameter leaving the graft with insufficient tissue strength, necessitating augmentation with soft tissue allograft. This can potentially lead to increased failure rates. Hamstring function and strength can also be permanently decreased, which can be detrimental to athletic performance, especially in the sprinting athlete. Decreased knee flexion strength and knee flexion ROM has been noted in previous meta-analysis to occur most frequently in hamstring grafts. Finally, infection rates have been reported to be higher in hamstring graft ACL reconstructions.

Finally, allograft reconstructions may have higher failure rates compared with autograft tissue in young, active patients. Previous study has reported allograft failure rates as high as 30%–40% in this population. Proponents of allograft use point to allograft sterilization and preparation as a potential confounding variable, that if done properly will normalize the failure rates. However, many surgeons avoid allograft usage either completely or at least in young athletes due to this reported increase in failure rates.