The bone attachments of the medial collateral and posterior oblique ligaments are defined anatomically and radiographically

Abstract

Purpose: To define the bony attachments of the medial ligaments relative to anatomical and radiographic bony landmarks, providing information for medial collateral ligament (MCL) surgery.

Method: The femoral and tibial attachments of the superficial MCL (sMCL), deep MCL (dMCL) and posterior oblique ligament (POL), plus the medial epicondyle (ME) were defined by radiopaque staples in 22 knees. These were measured radiographically and optically; the precision was calculated and data normalised to the sizes of the condyles. Femoral locations were referenced to the ME and to Blumensaat's line and the posterior cortex.

Results: The femoral sMCL attachment enveloped the ME, centred 1 mm proximal to it, at 37 ± 2 mm (normalised at 53 ± 2%) posterior to the most-anterior condyle border. The femoral dMCL attachment was 6 mm (8%) distal and 5 mm (7%) posterior to the ME. The femoral POL attachment was 4 mm (5%) proximal and 11 mm (15%) posterior to the ME. The tibial sMCL attachment spread from 42 to 71 mm (81-137% of A-P plateau width) below the tibial plateau. The dMCL fanned out anterodistally to a wide tibial attachment 8 mm below the plateau and between 17 and 39 mm (33-76%) A-P. The POL attached 5 mm below the plateau, posterior to the dMCL. The 95% CI intra-observer was ± 0.6 mm, inter-observer ± 1.3 mm for digitisation. The inter-observer ICC for radiographs was 0.922.

Conclusion: The bone attachments of the medial knee ligaments are located in relation to knee dimensions and osseous landmarks. These data facilitate repairs and reconstructions that can restore physiological laxity and stability patterns across the arc of knee flexion.

Keywords: Bone insertion attachment footprint; Knee anatomy; Medial collateral ligament; Posterior oblique ligament; Radiograph.

Fig. 1

Femoral attachments of the superficial MCL (sMCL), deep MCL (dMCL) and the posterior oblique ligament (POL) as seen radiographically, in relation to the normalisation as a percentage of the AP size of the medial femoral condyle. Note that the wire staples were inserted into the bone with the fold in the staple at the point of interest, and the radiographic study required identification of which end of each staple was the correct measurement point at the surface of the bone (coloured areas). The P-D measurements use the same 100% normalising length as the A-P measurements

Fig. 2

Tibial attachments of the superficial MCL (sMCL), deep MCL (dMCL) and the posterior oblique ligament (POL) as seen radiographically, in relation to the normalisation as a percentage of the A-P size (100%) of the medial tibial plateau, in both A-P and P-D directions. The arrow related to P-D measurement uses the same 100% length as the A-P measurements. Saw cuts for the elevation of a block of bone with the distal attachment of sMCL can be seen. The 2 distal screws have been used to fix the bone block back in place

Fig. 3

Method to define positions radiographically, using datum lines that (1) form an extension of the line of the posterior femoral cortex, and (2) a line perpendicular to the former passing through the most-posterior/proximal point of Blumensaat’s line [27]

Fig. 4

The femoral medial epicondyle, which was also the centre of the sMCL femoral attachment (marked as the black dot), was normalised in relation to the size of the medial femoral condyle: if mean A-P size of 69 mm was 100%, then the epicondyle was: 47% (32 mm) from both the posterior and distal and 53% (37 mm) from the anterior outline

Fig. 5

a The sMCL and PMC are shown with the knee in full extension. The medial epicondyle is at the red dot. The PMC/POL is taut with the knee in full extension (black arrow). b The sMCL and PMC/POL are shown with the knee flexed. The sMCL fibres (black arrow) centred their femoral attachment onto the medial epicondyle (red dot) and remained taut with knee flexion. The PMC/POL is slack with the knee flexed

Fig. 6

Mean limits of the soft tissue attachments relative to the medial epicondyle (ME-black dot) in a left knee as measured by optical digitisation, normalised to the size of the medial femoral condyle (MFC). The grid is offset so that it is centred at the ME at 53% posterior and 47% proximal to the edges of the MFC, as in Fig. 4. Data are superimposed onto a representative CT reconstruction. Data from the radiographic analysis (Table 1) were effectively the same when drawn in this manner, so are not shown

Fig. 7

Mean tibial attachment points of the superficial medial collateral ligament (sMCL), deep medial collateral ligament (dMCL) and posterior oblique ligament (POL) from optical digitisation measurements. Data are superimposed onto a representative CT reconstruction. Data from the radiographic analysis (Table 2) were effectively the same when drawn in this manner, so are not shown

Fig. 8

The mean positions (mm) of the centres of the ligament attachments relative to the medial epicondyle (ME). sMCL superficial medial collateral ligament, dMCL deep medial collateral ligament, POL posterior oblique ligament. a Anatomic orientation; b oriented as in surgery

Fig. 9

Medial aspect of a right knee in extension. The superficial medial collateral ligament (sMCL) has been elevated from distal (at the bottom of the picture) to proximal to display the deep medial collateral ligament (dMCL). The joint capsule has been split alongside the edges of the dMCL, revealing the femoral condyle. The lines across the femoral attachments of the ligaments show their A-P widths. The midpoint of the attachment of the dMCL is distal and posterior to the midpoint of the attachment of the sMCL. The fibres of the dMCL fan out distally and anteriorly to give a wide tibial attachment, making it ideally aligned to counter tibial external rotation

Fig. 10

a Medial aspect of a right knee. The superficial medial collateral ligament (sMCL) has been excised to display the deep medial collateral ligament (dMCL); the red dot is at the centre of the attachment of the sMCL. The femoral attachment of the dMCL is distal and posterior to the attachment of the sMCL. The joint capsule has been removed anterior and posterior to the edges of the dMCL, revealing the femoral condyle. In neutral tibial rotation the dMCL of this knee was oriented 24° from parallel to the long axis of the tibia at 15° knee flexion. b In external tibial rotation the dMCL of this knee was oriented 36° from parallel to the long axis of the tibia at 15° knee flexion

Fig. 11

The mean positions (to nearest mm) of the centres of the ligament attachments relative to the Schöttle point [27] at the extended posterior cortex of the femur and the most posterior point of Blumensaat’s line. sMCL superficial medial collateral ligament. dMCL deep medial collateral ligament, POL posterior oblique ligament. a Anatomical orientation, and b as in surgery