Effect of Lower Limb Alignment in Medial Meniscus-Deficient Knees on Tibiofemoral Contact Pressure

Abstract

Background: Degenerative medial meniscal tears and subsequent partial meniscal resection compromise meniscal function and lead to an overload of the medial compartment. In addition, lower limb alignment plays a key role in load distribution between the medial and lateral knee compartments, and varus alignment is a potential risk factor for medial osteoarthritis.

Purpose/hypothesis: The purpose of this biomechanical study was to investigate the effect of valgus and varus alignment on peak pressure and contact area in knees with concomitant horizontal medial meniscal tears and subsequent leaflet resection. It was hypothesized that varus alignment in combination with meniscal loss leads to the highest peak pressure within the medial compartment.

Study design: Controlled laboratory study.

Methods: Six fresh-frozen human cadaveric knees were axially loaded using a 1000-N compressive load in full extension with the mechanical axis rotated to intersect the tibial plateau at 40%, 45%, 50%, 55%, and 60% of its width (TPW) to simulate varus and valgus alignment. Tibiofemoral peak contact pressure and contact area of the medial and lateral compartments were determined using pressure-sensitive foils in each of 4 different meniscal conditions: intact, 15-mm horizontal tear of the posterior horn, inferior leaflet resection, and resection of both leaflets.

Results: The effect of alignment on peak pressure (normalized to the neutral axis) within the medial compartment in cases of an intact meniscus was measured as follows: varus shift resulted in a mean increase in peak pressure of 18.5% at 45% of the TPW and 37.4% at 40% of the TPW, whereas valgus shift led to a mean decrease in peak pressure of 8.7% at 55% of the TPW and 23.1% at 60% of the TPW. Peak pressure changes between the intact meniscus and resection within the medial compartment was less in valgus-aligned knees (0.21 MPa at 60% TPW, 0.59 MPa at 50% TPW, and 0.76 MPa at 40% TPW). Contact area was significantly reduced after partial meniscal resection in the neutral axis (intact, 553.5 ± 87.6 mm²; resection of both leaflets, 323.3 ± 84.2 mm²; P < .001). This finding was consistent in any alignment.

Conclusion: Both partial medial meniscal resection and varus alignment led to an increase in medial compartment peak pressure. Valgus alignment prevented medial overloading by decreasing contact pressure even after partial meniscal resection. A horizontal meniscal tear did not influence peak pressure and contact area even in varus alignment.

Clinical relevance: As a clinical consequence, partial meniscal resection should be avoided to maintain the original biomechanical behavior, and the mechanical axis should be taken into account if partial meniscectomy is necessary.

Keywords: biomechanical study; contact area; horizontal medial meniscal tear; peak pressure; tibiofemoral joint; valgus; varus.

Figure 1.

(A) Overview of the biomechanical alignment and compression setup (not to scale), consisting of (1) the center point of the femoral head, (2) the direction of the applied force, (3, 8) specimen potting, (4) laser projections for varus/neutral/valgus, (5) the distal femur, (6, 7) the proximal tibia and fibula, and (9) the ball bearing that can be shifted to meet the corresponding laser line. The amount of medial and lateral translation of the tibial fixation cap was calculated as: X = (B/A) × C. (B) Photograph depicting the virtual femoral head 50 cm above the joint line and the approximate 6° offset of the femoral anatomic axis to the potting casts. The neutral mechanical axis was defined as a strictly vertical connection between the center of the femoral head, the center of the tibial plateau, and the tibial ball bearing. Perpendicular laser lines imitating the Mikulicz line and the joint line monitored the medial and lateral shifts of the tibial fixation cap.

Figure 2.

A 15-mm horizontal meniscus tear was created and subsequently stepwise resected through a small posterior approach. A 3-mm rim remained to maintain the peripheral meniscal rim (*). mFC, medial femoral condyle; mTP, medial tibial plateau.

Figure 3.

Small changes in the mechanical axis (rotated to intersect the joint line at different percentages of the tibial plateau width) showed a significant change in peak pressure within the medial compartment (*P < .05).

Figure 4.

Summary of (A) peak pressure and (B) contact area as functions of the meniscal state and limb alignment in the medial compartment. (A) Peak pressure was significantly different between 40% of the tibial plateau width (TPW) and 60% of the TPW in the designated meniscal conditions (*P < .05). (B) Contact area was significantly reduced after single- and double-leaflet resection from the intact meniscus (*) and from the tear state (°) (P < .05).

Figure 5.

Visual representation of the peak pressure changes in the medial compartment depending on lower limb alignment with the intact meniscus and the Mikulicz line intersecting the tibial plateau at (A) 60%, (B) 55%, (C) 50%, (D) 45%, and (E) 40% of its width. Illustration of peak pressure changes in the medial compartment in the neutral axis with (F) an intact meniscus, (G) a horizontal tear, (H) single-leaflet resection, and (I) double-leaflet resection.

Figure 6.

Changes in peak pressure within the lateral compartment for the intact meniscus. A continuous decrease can be assumed when shifting the mechanical axis toward varus alignment (nonsignificant).