Contralateral Lateral Femoral Condyle Allografts Provide an Acceptable Surface Match for Simulated Classic Osteochondritis Dissecans Lesions of the Medial Femoral Condyle

Abstract

Objectives:

The purpose of this study was to determine whether contralateral lateral femoral condyle (LFC) allografts can provide an acceptable surface topography match for classic osteochondritis dessicans (OCD) lesions of the medial femoral condyle (MFC). Achievement of an acceptable donor-recipient articular surface match (1 mm deviation) has been associated with physiological joint stresses and predictably positive clinical outcomes. It was hypothesized that LFC and MFC allografts would show no differences in step-off height or surface deviation in all four quadrants of the graft.

Methods:

ample size calculation suggested ten groups of fresh frozen size-matched human condyles, each group consisting of a donor MFC, donor LFC, and recipient MFC. A 20 mm circular osteochondral “defect” simulating a “classic” OCD lesion was created in the recipient MFC. Its most anterior position was 1 cm posterior and 1 cm medial to the roof of the intercondylar notch. A randomly selected donor MFC or LFC plug was then harvested and transplanted using standard procedure (Fig 1A). The transplanted condyle was scanned with nano-CT, reconstructed (Fig 1B), registered to an initial scan of the recipient MFC, and processed with a custom MATLAB program to determine the surface root mean squared deviation (d_RMS) between the native and donor surfaces (Fig 1C), percent area unacceptably proud (>1 mm; %A_proud) and sunken (<-1 mm; %A_sunk). Scans were uploaded into DragonFly software where step-off height (h_RMS), percent circumference unacceptably proud (>1 mm; %C_proud) and sunken (< -1 mm; %C_sunk) were measured (Fig 1D). The process was then repeated for the other allograft plug. Two-way mixed ANOVAs with Sidak corrections for multiple comparisons (α=0.05) were used. Exempt status was obtained from the University’s IRB.

Results:

Both MFC and LFC plugs showed acceptable step-off heights in all four quadrants. Neither allograft type nor location within the defect had a main effect on step-off height (h_RMS). In general, plugs were more unacceptably sunken than proud, though no differences in %C_sunk were seen between allograft types or locations within the defect. In LFC plugs, %C_proud was significantly greater laterally (by the intercondylar notch) compared to all other locations around the plug (p<0.0001), while no differences were seen based on location in MFC plugs. The cartilage surface deviationn (d_RMS), %A_proud, and %A_sunk were not significantly affected by allograft type or location (Table 1).

Conclusion:

Previous studies demonstrated that contralateral LFCs provide acceptable surface topography matches for centrally located defects of the MFC. In evaluating the utility of LFC allografts for more laterally located lesions characteristic of OCD, it was found that, similarly, allograft type does not have an effect on surface deviation or step-off height. With comparable surface deviations, both MFC and LFC allografts can be expected to present similar stresses on the knee joint and achieve predictably positive clinical outcomes, thus improving donor availability and reducing surgical wait times for matches. LFC plugs did not differ from MFC plugs in overall %A_proud, %A_sunk, %C_proud, or %C_sunk suggesting that well placed LFC plugs, like MFC plugs, may result in few post-surgical complications. Higher step-off heights of LFC plugs near the intercondylar notch may contribute to higher joint stresses and may serve as an area of focus in future studies.

Figure 1.

(A) en-face view of transplanted osteochondral allograft adjacent to the intercondylar notch. (B) 3D reconstruction of nano-CT image showing the four regional quadrants of the allograft considered in this study. (C) Example color map of surface deviation of transplanted condyle relative to native condyle (scale: in mm). (D) Example of a sunken plug: h_RMS measured between plug and native cartilage surfaces (white arrow)

Table 1:

Step-off height and surface deviation measurements for anterior, posterior, medial, and lateral quadrants of the medial (MFC) and lateral (LFC) allgrafts. (*) is significantly different from (^t) when comparing locations in a particular allograft type (p<0.05). Data presented as mean ± standard deviation.

	MFC					LFC
	Anterior	Medial	Posterior	Lateral	Overall	Anterior	Medial	Posterior	Lateral	Overall
hRMS (mm)	0.62 ± 0.33	0.59 ± 0.33	0.58 ± 0.20	0.64 ± 0.42	0.63 ± 0.24	0.76 ± 0.36	0.53 ± 0.18	0.64 ± 0.45	0.94 ± 0.40	0.74 ± .12
%Cproud	0.00 ± 0.00	0.00 ± 0.00	1.67 ± 5.3	11.3 ± 27.0	2.42 ± 7.64	2.00 ± 5.26^t	1.33 ± 4.22^t	0.00 ± 0.00^t	28.0 ± 26.1*	8.08 ± 6.89
%Csunk	18.0 ± 27.9	17.7 ± 31.9	7.00 ± 15.3	11.0 ± 24.7	13.4 ± 17.9	26.0 ± 33.1	3.67 ± 7.77	16.7 ± 36.0	4.67 ± 7.06	13.2 ± 14.5

dRMS(mm)	0.49 ± 0.30	0.45 ± 0.21	0.47 ± 0.27	0.55 ± 0.26	0.51 ± 0.22	0.53 ± 0.38	0.61 ± 0.31	0.49 ± 0.31	0.53 ± 0.28	0.57 ± 0.25
%Aproud	4.38 ± 132	0.00 ± 0.00	0.00 ± 0.00	7.12 ± 11.8	3.16 ± 5.28	2.21 ± 4.52	15.1 ± 23.1	3.88 ± 11.7	5.06 ± 15.2	6.12 ± 10.6
%Asunk	2.42 ± 7.25	2.20 ± 5.96	9.41 ± 28.2	1.32 ± 3.97	3.63 ± 7.94	9.48 ± 28.1	2.11 ± 4.82	10.1 ± 30.2	5.18 ± 10.5	6.08 ± 12.1