AJSM - 2026-06-05 - Journal Article
In Vitro Evaluation of Tibiofemoral Contact Stress and Graft Loading After Modified MacIntosh Anterior Cruciate Ligament Reconstruction.
Bram JT, Shamritsky DZ, Mange TR, Bae LE, Beber SA, Imhauser CW, Fabricant PD
Topics
Key Takeaway
Modified MacIntosh ACLR increases lateral compartment peak contact stress by 0.31–0.35 MPa and anteriorizes the center of contact stress by 1.3–3.3 mm versus intact knee, while the intra-articular graft carries only 27–36 N (51–65% less than native ACL force) during simulated pivot shift.
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Summary
This study quantified tibiofemoral contact mechanics, laxity, and graft loading in cadaveric knees tested in intact, ACL-sectioned, and modified MacIntosh ACLR states using a robotic manipulator with simulated pivot-shift loading. Modified MacIntosh ACLR restored lateral compartment contact stress below ACL-deficient levels but did not fully normalize it versus intact, with a residual 0.31–0.35 MPa increase and 1.3–3.3 mm anterior shift in center of contact stress. The extra-articular component carried 25–30 N during pivot shift, and the construct over-constrained internal rotation and varus laxity by 18–24% and 13–24%, respectively, compared to the intact knee.
Key Limitation
The n=8 cadaveric sample with mean age 56 years limits statistical power and direct applicability to the pediatric and adolescent patients who actually undergo this procedure.
Original Abstract
BACKGROUND
The modified MacIntosh anterior cruciate ligament reconstruction (ACLR) consists of a combined intra- and extra-articular construct using iliotibial band autograft. It is used in skeletally immature patients to avoid physeal injury. However, its effect on articular cartilage contact mechanics, rotational laxity, and graft loading is poorly understood.
HYPOTHESIS
Relative to the intact knee, a modified MacIntosh ACLR would (1) increase and anteriorize lateral tibiofemoral contact stress, (2) decrease internal rotation (IR) and varus laxity, and (3) offload the intra-articular graft relative to the native ACL in response to simulated pivot-shift loads.
STUDY DESIGN
Controlled laboratory study.
METHODS
Eight cadaveric knees (mean age 56 ± 7 years; 50% male) were tested on a robotic manipulator in 3 states: intact, ACL-sectioned, and modified MacIntosh ACLR. Peak contact stress and the anterior-posterior position of the center of contact stress (CCS) in the lateral compartment were calculated during simulated pivot shifts. Laxity was assessed for 3 uniplanar loading conditions (134 N anterior, 8 N·m varus, and 5 N·m IR) at knee flexion angles from 0° to 90°. Tissue forces were determined via the principle of superposition.
RESULTS
After modified MacIntosh ACLR, peak stress increased by 0.31 to 0.35 MPa ( P < .03) and the CCS shifted anteriorly by 1.3 to 3.3 mm ( P < .05) relative to the intact knee. ACLR decreased IR and varus laxity by 18% to 24% ( P ≤ .01) and 13% to 24% ( P < .02), respectively, compared with the intact state. During simulated pivot shift, in situ force in the intra-articular graft component (27 to 36 N) was 51% to 65% less than native ACL force, whereas the extra-articular component carried 25 to 30 N.
CONCLUSION
In a cadaveric model of a simulated pivot shift, a modified MacIntosh ACLR anteriorized and mildly increased lateral compartment contact stress compared to the native knee, while decreasing lateral compartment contact stress relative to the ACL-deficient knee. The extraarticular limb also increased constraint to rotational loads, partially offloading the intra-articular graft.
CLINICAL RELEVANCE
Partial intraarticular graft offloading with clinical pivoting maneuvers provides a biomechanical rationale for the low number of graft failures after modified MacIntosh ACLR. The ability of a modified MacIntosh ACLR to decrease and anteriorize contact stress in the posterior aspect of the lateral compartment offloads the region most affected by ACL injury and the pivot shift contact. Long-term clinical studies are needed to determine whether altered contact mechanics after modified MacIntosh ACLR influence long-term cartilage health.