Graft Selection in ACL Reconstructive Surgery
Graft Selection in ACL Reconstructive Surgery
The advantages and disadvantages of each graft option have been discussed in details. Although many different options have been demonstrated in this review, the autogenous grafts are still the most valuable options in ACL reconstructive surgery and can be suggested as a gold standard in ACL reconstruction. Generally, this statement is in agreement with most of the reviews and research articles published in the last decade. Despite previous studies, allografts are an option in ACL reconstructive surgery and should be selected when limitation of autogenous grafts would be of great concern for the patient. To date, there is no well-accepted opinion about the best graft options among the autogenous grafts. Perhaps the controversies are the most significant issues in this point, and some potential bias and conflicts of interests should be considered to explain these controversies. Additionally, individual variations in the patients, such as age, sex, and life style as well as the surgical methods, could significantly affect the outcome of the studies and should not be dismissed. This review suggests that patellar tendons and hamstring tendons are the gold standard for ACL reconstructive surgery; however, the final decision should be made by the surgeon. As we mentioned in this review, both patellar tendon and hamstring tendon autografts have some advantages and disadvantages, and here we compared the overall outcome of these autografts options and entrust the final decision to the readers.
Clinical studies have demonstrated that these two graft choices have similar rates of effectiveness in adults, with minor differences in postreconstruction knee stability, and muscle strength and activity levels at 2 and 5 years after implantation. Li et al. demonstrated that ACL reconstruction with hamstring tendon or bone-patellar tendon-bone autografts achieved similar postoperative effects in terms of restoring knee joint function. Hamstring tendon autografts were inferior to bone-patellar tendon-bone autografts for restoring knee joint stability but were associated with fewer postoperative complications. In a recent study, Gifstad et al. evaluated 114 patients with asymptomatic ACL rupture after they were randomly reconstructed with either a patellar tendon (n=58) or a hamstring tendon (n=56) graft. Their results showed that both grafts resulted in satisfactory subjective outcome and objective stability, and there were no significant differences between these surgical procedures.
The methods of preparation of the hamstring tendon grafts (1–4 strands) could determine the clinical outcome and make this graft type comparable or even better than the gold standard patellar tendon grafts. The structural strength of a hamstring tendon graft, with all four strands equally tensioned at time zero (4590 N), is superior to that of a 10-mm bone-patellar tendon-bone graft (2977 N). In a recent prospective longitudinal study, Leys et al. compared the results of isolated endoscopic ACL reconstruction using a four-strand hamstring tendon or patellar tendon autograft over a 15-year period with respect to reinjury, clinical outcomes, and development of osteoarthritis. Patients who received the patellar tendon graft had significantly worse outcomes compared with those who received the hamstring tendon graft for the variables of radiographically detectable osteoarthritis (P=0.04), motion loss (P=0.03), single-legged hop test (P=0.001), participation in strenuous activity (P=0.04), and kneeling pain (P=0.04). ACL graft rupture occurred in 17% of the hamstring tendon group and 8% of the patellar tendon group (P=0.07). The ACL graft rupture was associated with nonideal tunnel position and male sex. Contralateral ACL rupture occurred in significantly more patients with patellar tendon grafts than patients with hamstring tendon grafts (P=0.02). Their results showed that the hamstring tendon autograft had better outcomes than the patellar tendon autograft in all these outcome measures. Additionally, at 15 years, the hamstring tendon graft-reconstructed ACLs have shown a lower rate of radiographic osteoarthritis. In another experiment, Genuario et al. showed that ACL reconstruction with hamstring tendon autograft is the most cost-effective method of surgery for the average patient with ACL deficiency.
O'Neill compared three techniques for ACL reconstruction. One hundred twenty-seven patients with a torn ACL received either a single or two-incisional reconstruction using patellar tendon graft, or a two-incision reconstruction using a double-stranded hamstring tendon graft. The patients who were treated with a two-incisional reconstruction using a patellar tendon graft returned to a greater level of athletic activity than the other two groups, and a higher percentage of the patients in this group had satisfactory stability. Aglietti et al. compared the two grafts by alternating graft choice in nonrandomized patients. The PT grafts were fixed by use of a post and washer on the femoral side and an interference screw on the tibial side, whereas the hamstring tendon grafts were fixed with a post and washer outside the femoral and tibial channels. Patellofemoral crepitation and minor loss of extension were more common among patients in the patellar tendon group. Return to sports was more frequent among the patients in the patellar tendon group. There were no differences in the incidence of symptoms or laxity between the groups.
Mohtadi et al. compared the clinical outcome of 1597 young to middle-aged adults who underwent patellar tendon or hamstring tendon reconstruction and showed that the patellar tendon group resulted in a more statically stable knee compared with hamstring tendon reconstruction (P<0.05). Conversely, patients experienced more anterior knee problems, especially with kneeling after patellar tendon reconstruction. Patellar tendon reconstructions resulted in a statistically significant loss of extension range of motion and a trend towards loss of knee extension strength. Hamstring tendon reconstructions demonstrated a trend towards loss of flexion range of motion and a statistically significant loss of knee flexion strength. The clinical importance of the above range of motion losses is unclear. Although their study was comprehensive, they failed to conclude which graft was the best in the long-term. They just concluded that while patellar tendon reconstructions are more likely to result in statically stable knees, they also are associated with more anterior knee problems.
One of the major limitations of hamstring tendon grafts compared with patellar tendon grafts is their low healing ability. Janssen et al. studied 67 patients who underwent retrieval of midsubstance biopsies after clinically successful hamstring autograft ACL reconstruction. Human hamstring grafts showed typical stages of graft remodeling, which was not complete up to 2 years after reconstruction. The remodeling process in humans was prolonged compared with the results obtained in several animal studies. So, in this case the animal studies were of low value, and their results could not be extrapolated with confidence to humans.
The hamstring tendon autografts are possibly better options than patellar tendon ones if the anchorage techniques and tendon-to-bone healing is improved. Despite variable techniques aiming to improve bone tunnel healing, bone morphogenetic protein (BMP) and calcium phosphate cement are still mainstays of treatment for optimization of the healing process in this purpose. In a recent study, Hashimoto et al. attempted to generate a bone-tendon-bone structure by injecting human-type recombinant human bone morphogenetic protein-2 (rhBMP-2) into the hamstring tendons, and the ACL defect was reconstructed by grafting the engineered bone-tendon-bone graft. Biomechanical pull-out testing showed that the ultimate failure load and stiffness of the reconstructed ACL in the experimental group were significantly higher than those in the control group at both 4 and 8 weeks (P<0.05). These results indicate the potential of regenerative reconstruction of the ACL, and the reconstruction resulted in restoration of morphology and function equivalent to those of a normal ACL. Pan et al. also compared the effect of osteointegration of grafted tendon in bone tunnels between the injected calcium phosphate cement (ICPC) and injected fibrin sealant (IFS) combined with BMP after ACL reconstruction in 51 rabbits. After 2, 6, and 12 weeks, biomechanically, the ultimate failure load in the ICPC-BMP group was always higher than that in the IFS-BMP group. It is evident that the ICPC composite achieved a more prolonged osteogenic effect than that by IFS composite. Nebelung et al. evaluated midterm outcomes after transfemoral graft fixation using either a conventional or a modified technique and additional bone plug augmentation (BPA) of the femoral tunnel aperture after ACL reconstruction with a quadrupled hamstring autograft in 56 patients. They found that additional BPA has the capacity to improve morphological and clinical outcomes at 5-year follow-up.
Allografts also are valuable options if the limitations of autogenous grafts are of great concern to patients. Kim et al. evaluated the effect of hamstring harvesting in 73 consecutive patients who underwent ACL reconstruction. Thirty-nine patients whose hamstrings were harvested for autografts were compared with 34 patients who received allografts during the same time period. Their results indicated significant knee flexion weakness compared with the unaffected knee after ACL reconstruction regardless of hamstring harvesting. Moreover, the greater increase in knee flexor deficit in the hamstring-harvested group compared with the allograft group was statistically significant. However, the clinical and functional outcomes were similar between the groups. Aslan et al. investigated the clinical outcome of ACL reconstructions with allograft or autograft. They evaluated 82 patients who underwent arthroscopic ACL reconstruction with patellar tendon allograft (n=52) or hamstring tendon autograft (n=30). The patients were assessed using the International Knee Documentation Committee (IKDC) and Lysholm knee scores and functional (one-leg hop) and laxity (pivot-shift, Lachman, anterior drawer) tests. There was no statistically significant difference between the groups with respect to IKDC and Lysholm scores, functionality and ligament laxity (P>0.05). However, effusions were more frequent in the hamstring tendon group compared with the patellar tendon group. They showed that differences in graft options for ACL reconstruction have no effect on the clinical outcome. In another more recent study, Rice et al. determined the optimal decision between autograft and allograft for patients undergoing ACL reconstruction. Expected-value decision and sensitivity analyses were performed to systematically quantify the clinical decision. Their results indicated that autograft is preferred over allograft for ACL surgical reconstruction. Pallis et al. showed that in a young, active cohort, individuals having undergone an ACL reconstruction using allograft were significantly more likely to experience clinical failure, requiring revision reconstruction compared with those who underwent autologous graft reconstruction. They recommended autograft use in ACL reconstruction in young athletes.
Xenografts, synthetic, hybrid, and tissue-engineered grafts are still under investigation but it seems that some of them may be considered as the future options. For now, they are not recommended for ACL reconstruction in human beings.16,68–74
Definitive Argument About Available Graft Choices
The advantages and disadvantages of each graft option have been discussed in details. Although many different options have been demonstrated in this review, the autogenous grafts are still the most valuable options in ACL reconstructive surgery and can be suggested as a gold standard in ACL reconstruction. Generally, this statement is in agreement with most of the reviews and research articles published in the last decade. Despite previous studies, allografts are an option in ACL reconstructive surgery and should be selected when limitation of autogenous grafts would be of great concern for the patient. To date, there is no well-accepted opinion about the best graft options among the autogenous grafts. Perhaps the controversies are the most significant issues in this point, and some potential bias and conflicts of interests should be considered to explain these controversies. Additionally, individual variations in the patients, such as age, sex, and life style as well as the surgical methods, could significantly affect the outcome of the studies and should not be dismissed. This review suggests that patellar tendons and hamstring tendons are the gold standard for ACL reconstructive surgery; however, the final decision should be made by the surgeon. As we mentioned in this review, both patellar tendon and hamstring tendon autografts have some advantages and disadvantages, and here we compared the overall outcome of these autografts options and entrust the final decision to the readers.
Clinical studies have demonstrated that these two graft choices have similar rates of effectiveness in adults, with minor differences in postreconstruction knee stability, and muscle strength and activity levels at 2 and 5 years after implantation. Li et al. demonstrated that ACL reconstruction with hamstring tendon or bone-patellar tendon-bone autografts achieved similar postoperative effects in terms of restoring knee joint function. Hamstring tendon autografts were inferior to bone-patellar tendon-bone autografts for restoring knee joint stability but were associated with fewer postoperative complications. In a recent study, Gifstad et al. evaluated 114 patients with asymptomatic ACL rupture after they were randomly reconstructed with either a patellar tendon (n=58) or a hamstring tendon (n=56) graft. Their results showed that both grafts resulted in satisfactory subjective outcome and objective stability, and there were no significant differences between these surgical procedures.
The methods of preparation of the hamstring tendon grafts (1–4 strands) could determine the clinical outcome and make this graft type comparable or even better than the gold standard patellar tendon grafts. The structural strength of a hamstring tendon graft, with all four strands equally tensioned at time zero (4590 N), is superior to that of a 10-mm bone-patellar tendon-bone graft (2977 N). In a recent prospective longitudinal study, Leys et al. compared the results of isolated endoscopic ACL reconstruction using a four-strand hamstring tendon or patellar tendon autograft over a 15-year period with respect to reinjury, clinical outcomes, and development of osteoarthritis. Patients who received the patellar tendon graft had significantly worse outcomes compared with those who received the hamstring tendon graft for the variables of radiographically detectable osteoarthritis (P=0.04), motion loss (P=0.03), single-legged hop test (P=0.001), participation in strenuous activity (P=0.04), and kneeling pain (P=0.04). ACL graft rupture occurred in 17% of the hamstring tendon group and 8% of the patellar tendon group (P=0.07). The ACL graft rupture was associated with nonideal tunnel position and male sex. Contralateral ACL rupture occurred in significantly more patients with patellar tendon grafts than patients with hamstring tendon grafts (P=0.02). Their results showed that the hamstring tendon autograft had better outcomes than the patellar tendon autograft in all these outcome measures. Additionally, at 15 years, the hamstring tendon graft-reconstructed ACLs have shown a lower rate of radiographic osteoarthritis. In another experiment, Genuario et al. showed that ACL reconstruction with hamstring tendon autograft is the most cost-effective method of surgery for the average patient with ACL deficiency.
O'Neill compared three techniques for ACL reconstruction. One hundred twenty-seven patients with a torn ACL received either a single or two-incisional reconstruction using patellar tendon graft, or a two-incision reconstruction using a double-stranded hamstring tendon graft. The patients who were treated with a two-incisional reconstruction using a patellar tendon graft returned to a greater level of athletic activity than the other two groups, and a higher percentage of the patients in this group had satisfactory stability. Aglietti et al. compared the two grafts by alternating graft choice in nonrandomized patients. The PT grafts were fixed by use of a post and washer on the femoral side and an interference screw on the tibial side, whereas the hamstring tendon grafts were fixed with a post and washer outside the femoral and tibial channels. Patellofemoral crepitation and minor loss of extension were more common among patients in the patellar tendon group. Return to sports was more frequent among the patients in the patellar tendon group. There were no differences in the incidence of symptoms or laxity between the groups.
Mohtadi et al. compared the clinical outcome of 1597 young to middle-aged adults who underwent patellar tendon or hamstring tendon reconstruction and showed that the patellar tendon group resulted in a more statically stable knee compared with hamstring tendon reconstruction (P<0.05). Conversely, patients experienced more anterior knee problems, especially with kneeling after patellar tendon reconstruction. Patellar tendon reconstructions resulted in a statistically significant loss of extension range of motion and a trend towards loss of knee extension strength. Hamstring tendon reconstructions demonstrated a trend towards loss of flexion range of motion and a statistically significant loss of knee flexion strength. The clinical importance of the above range of motion losses is unclear. Although their study was comprehensive, they failed to conclude which graft was the best in the long-term. They just concluded that while patellar tendon reconstructions are more likely to result in statically stable knees, they also are associated with more anterior knee problems.
One of the major limitations of hamstring tendon grafts compared with patellar tendon grafts is their low healing ability. Janssen et al. studied 67 patients who underwent retrieval of midsubstance biopsies after clinically successful hamstring autograft ACL reconstruction. Human hamstring grafts showed typical stages of graft remodeling, which was not complete up to 2 years after reconstruction. The remodeling process in humans was prolonged compared with the results obtained in several animal studies. So, in this case the animal studies were of low value, and their results could not be extrapolated with confidence to humans.
The hamstring tendon autografts are possibly better options than patellar tendon ones if the anchorage techniques and tendon-to-bone healing is improved. Despite variable techniques aiming to improve bone tunnel healing, bone morphogenetic protein (BMP) and calcium phosphate cement are still mainstays of treatment for optimization of the healing process in this purpose. In a recent study, Hashimoto et al. attempted to generate a bone-tendon-bone structure by injecting human-type recombinant human bone morphogenetic protein-2 (rhBMP-2) into the hamstring tendons, and the ACL defect was reconstructed by grafting the engineered bone-tendon-bone graft. Biomechanical pull-out testing showed that the ultimate failure load and stiffness of the reconstructed ACL in the experimental group were significantly higher than those in the control group at both 4 and 8 weeks (P<0.05). These results indicate the potential of regenerative reconstruction of the ACL, and the reconstruction resulted in restoration of morphology and function equivalent to those of a normal ACL. Pan et al. also compared the effect of osteointegration of grafted tendon in bone tunnels between the injected calcium phosphate cement (ICPC) and injected fibrin sealant (IFS) combined with BMP after ACL reconstruction in 51 rabbits. After 2, 6, and 12 weeks, biomechanically, the ultimate failure load in the ICPC-BMP group was always higher than that in the IFS-BMP group. It is evident that the ICPC composite achieved a more prolonged osteogenic effect than that by IFS composite. Nebelung et al. evaluated midterm outcomes after transfemoral graft fixation using either a conventional or a modified technique and additional bone plug augmentation (BPA) of the femoral tunnel aperture after ACL reconstruction with a quadrupled hamstring autograft in 56 patients. They found that additional BPA has the capacity to improve morphological and clinical outcomes at 5-year follow-up.
Allografts also are valuable options if the limitations of autogenous grafts are of great concern to patients. Kim et al. evaluated the effect of hamstring harvesting in 73 consecutive patients who underwent ACL reconstruction. Thirty-nine patients whose hamstrings were harvested for autografts were compared with 34 patients who received allografts during the same time period. Their results indicated significant knee flexion weakness compared with the unaffected knee after ACL reconstruction regardless of hamstring harvesting. Moreover, the greater increase in knee flexor deficit in the hamstring-harvested group compared with the allograft group was statistically significant. However, the clinical and functional outcomes were similar between the groups. Aslan et al. investigated the clinical outcome of ACL reconstructions with allograft or autograft. They evaluated 82 patients who underwent arthroscopic ACL reconstruction with patellar tendon allograft (n=52) or hamstring tendon autograft (n=30). The patients were assessed using the International Knee Documentation Committee (IKDC) and Lysholm knee scores and functional (one-leg hop) and laxity (pivot-shift, Lachman, anterior drawer) tests. There was no statistically significant difference between the groups with respect to IKDC and Lysholm scores, functionality and ligament laxity (P>0.05). However, effusions were more frequent in the hamstring tendon group compared with the patellar tendon group. They showed that differences in graft options for ACL reconstruction have no effect on the clinical outcome. In another more recent study, Rice et al. determined the optimal decision between autograft and allograft for patients undergoing ACL reconstruction. Expected-value decision and sensitivity analyses were performed to systematically quantify the clinical decision. Their results indicated that autograft is preferred over allograft for ACL surgical reconstruction. Pallis et al. showed that in a young, active cohort, individuals having undergone an ACL reconstruction using allograft were significantly more likely to experience clinical failure, requiring revision reconstruction compared with those who underwent autologous graft reconstruction. They recommended autograft use in ACL reconstruction in young athletes.
Xenografts, synthetic, hybrid, and tissue-engineered grafts are still under investigation but it seems that some of them may be considered as the future options. For now, they are not recommended for ACL reconstruction in human beings.16,68–74
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