Cartilage and chondrocyte response to extreme muscular loading and impact loading: Can in vivo pre-load decrease impact-induced cell death?

Douglas A Bourne,Eng Kuan Moo,Walter Herzog

doi:10.1016/j.clinbiomech.2015.04.009

Abstract

BackgroundImpact loading causes cartilage damage and cell death. Pre-loading prior to impact loading may protect cartilage and chondrocytes. However, there is no systematic evidence and understanding of the effects of pre-load strategies on cartilage damage and chondrocyte death. This study aimed at determining the effects of the pre-load history on impact-induced chondrocyte death in an intact joint. MethodsPatellofemoral joints from 42 rabbits were loaded by controlled quadriceps muscle contractions and an external impacter. Two extreme muscular loading conditions were used: (i) a short-duration, high intensity, static muscle contraction, and (ii) a long-duration, low-intensity, cyclic muscle loading protocol. A 5-Joule centrally-oriented, gravity-accelerated impact load was applied to the joints. Chondrocyte viability was quantified following the muscular loading protocols, following application of the isolated impact loads, and following application of the impact loads that were preceded by the muscular pre-loads. Joint contact pressures were measured for all loading conditions by a pressure-sensitive film. FindingsComparing to cartilage injured by impact loading alone, cartilage pre-loaded by static, maximal intensity, short-term muscle loads had lower cell death, while cartilage pre-loaded by repetitive, low-intensity, long-term muscular loads has higher cell death. The locations of peak joint contact pressures were not strongly correlated with the locations of greatest cell death occurrence. InterpretationStatic, high intensity, short muscular pre-load protected cells from impact injury, whereas repetitive, low intensity, prolonged muscular pre-loading to the point of muscular fatigue left the chondrocytes vulnerable to injury. However, cell death seems to be unrelated to the peak joint pressures.

Highlights

Injuries to cartilage are thought to trigger the development of a debilitating joint disease called post-traumatic osteoarthritis (PTOA) (Anderson et al, 2011; Dirschl et al, 2004)
The maximally-stimulated rabbit quadriceps muscles produced forces of 361±13N; the submaximally-stimulated muscles generated average forces of 72±5N. For both extreme muscular loading protocols applied here, we observed a tendency for increased cell death in the cartilage of the patella and femoral groove compared to the corresponding control cartilages of the no-load group animals (Fig. 3)
Cartilage pre-loaded by a maximal muscular contraction prior to and during impact loading had a decreased percentage of cell death (Fig. 5) compared to the corresponding cartilages receiving impact loading alone

Summary

Introduction

Injuries to cartilage are thought to trigger the development of a debilitating joint disease called post-traumatic osteoarthritis (PTOA) (Anderson et al, 2011; Dirschl et al, 2004). (Chen et al, 2001a; Dirschl et al, 2004; Ewers et al, 2001; Krueger et al, 2003; Lewis et al., 2003; Rundell et al, 2005; Szczodry et al, 2009) Such fissures result in mechanical weakening and associated loss of protective properties for the chondrocytes. If ECM damage is substantial, it typically results in cell death and associated degeneration of the adjacent cartilage tissue (Shlopov et al, 1997). This study aimed at determining the effects of the pre-load history on impact-induced chondrocyte death in an intact joint

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