Evaluating Thigh Muscle Volume and Compensatory Muscle Changes in Bone–Patellar Tendon–Bone, Hamstring Autograft, and Allograft Anterior Cruciate Ligament Reconstructions: A Minimum 5-Year Follow-up

Background: Graft selection in anterior cruciate ligament reconstruction (ACLR) may lead to long-term, graft-specific muscle adaptations, yet their effect on functional outcomes remains poorly understood. Magnetic resonance imaging (MRI)–based 3D modeling enables precise quantification of muscle volume changes, offering insight into the relationship between postoperative muscle preservation and patient-reported outcomes. Purpose: To radiologically evaluate thigh muscle volume changes and patient-reported outcomes at minimum 5-year follow-up among patients after primary anterior cruciate ligament reconstruction (ACLR) using allograft, bone–patellar tendon–bone autograft (BPTB), or hamstring autograft (gracilis and semitendinosus; HS) with MRI-based 3D modeling. Study Design: Cohort study; Level of evidence, 3. Methods: Patients aged 18 to 45 years (mean ± SD age, 26.9 ± 7.2 years) with a body mass index (BMI) <30 who underwent primary ACLR with either allograft, BPTB, or HS with minimum 5-year follow-up were identified via retrospective chart review. Exclusion criteria were any history of a knee flexor or extensor injury/surgery, revision ACLR procedures, any concomitant surgical procedures other than chondral debridement and/or meniscectomy/repair, or any subsequent lower extremity surgery since the index ACLR. Bilateral thigh 3.0-T MRI scans were obtained, and images were rendered using 3D modeling software. Volume measurements were performed for (1) the individual muscles, (2) each compartment, and (3) the entire thigh. Specific individual muscles analyzed included the quadriceps (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) and sartorius in the anterior compartment; the hamstrings (biceps femoris long and short heads, semitendinosus, semimembranosus) in the posterior compartment; and the gracilis and combined adductor muscle group in the medial compartment. Individual muscle volumes were calculated for each thigh and then normalized as a percentage of the total volume of their respective muscle compartments. These compartment-relative percentages in the operative thigh were subsequently compared with the corresponding percentages in the contralateral, nonoperative thigh. Multivariable linear regression linked ratios of injured to contralateral muscle preservation (total and compartmental) to International Knee Documentation Committee (IKDC) scores, adjusting for age, sex, BMI, and graft type. Paired Student t tests and chi-square tests were used for statistical analysis. Results: A total of 30 patients were included: 10 allograft, 10 BPTB, and 10 HS. The cohort consisted of 18 male patients (60%) and 12 female patients (40%), with a higher proportion of male patients in the BPTB group (9/10 male). Allograft patients (mean age, 34.6 years; range, 31-40 years) were significantly older at surgery than BPTB (mean age, 23.4 years; range, 17-33 years) and HS cohorts (mean age, 22.7 years; range, 16-28 years) ( P < .001). The mean time interval from surgery to follow-up MRI was 6.7 ± 1.2 years. No significant differences in total thigh or individual muscle volumes were found between operative and nonoperative limbs with allograft. BPTB demonstrated a significant reduction in mean muscle volume percentage of the vastus intermedius in the operative thigh compared with the nonoperative thigh (13.98% vs 16.48%; P < .001). With HS, significant reductions were observed in mean muscle volume percentages of the gracilis (15.61% vs 27.35%; P < .001) and semitendinosus (7.49% vs 17.49%; P = .001) muscles in the operative thigh. Conversely, the semimembranosus exhibited a significant increase in mean muscle volume percentage in the operative thigh relative to the nonoperative thigh (42.50% vs 36.57%; P = .006). Across graft types, greater preservation of operative-limb muscle volume predicted better function: Total-thigh preservation correlated with higher IKDC scores ( B = 61.8; P = .043), and anterior-compartment preservation showed the strongest association ( B = 110.3; P = .004; model R 2 = 0.48). No covariate (age, sex, BMI, graft type) independently influenced IKDC score. Conclusion: Five years after ACLR, thigh muscle adaptation depended on graft choice and carried meaningful functional consequences. Hamstring autografts were associated with lasting atrophy of the semitendinosus and gracilis with compensatory hypertrophy of the semimembranosus, whereas BPTB autografts were associated with selective loss of the vastus intermedius and no compensatory enlargement in the remaining quadriceps. Across all patients, larger differences in muscle volume between limbs, especially in the anterior compartment, were linked to lower IKDC scores.