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

BACKGROUND: Impact 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. METHODS: Patellofemoral 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. FINDINGS: Comparing 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. INTERPRETATION: Static, 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.

The placement of skin surface markers for non-invasive measurement of scapular kinematics affects accuracy and reliability.

Abnormal scapular movement is widely believed to be an important factor in clinical pathology of the shoulder joint complex. Validated non-invasive techniques for measuring scapular movement have been developed, but the effect of marker placement on accuracy is unknown. The objective of this study was to determine the accuracy and reliability of different groupings of markers to achieve the best accuracy and reliability for measuring scapular kinematics. Eight healthy young adult subjects were recruited. An optoelectronic marker grid was applied to the skin overlying the scapula. Two bone pins with optoelectronic marker carriers were inserted into the scapula. The accuracy of six surface marker configurations was determined by comparing the measured kinematics with scapular bone pins (the gold standard). Four humeral movements were tested: glenohumeral abduction, glenohumeral horizontal adduction, hand behind back, and forward reaching. All three rotations had a significant difference in the accuracy of the patches (p = 0.04 to p < 0.0001). For posterior tipping there was a significant effect of movement (p = 0.003) and a significant interaction (p < 0.0001). There was also a significant interaction for external rotation (p = 0.001). The marker grouping with the largest cranio-caudal spread had the highest accuracy for measuring posterior tilting (RMS 1.9°). Markers closer to the scapular spine were more accurate for tracking external rotation (RMS 2.0°) while an intermediate grouping of markers were most accurate for quantifying upward rotation (RMS 1.9°). The reliability between days ranged between 3.8° and 7.5° (based on RMS difference between trials) and there was a significant interaction between patch and movement (p < 0.0001). Intraclass correlation coefficients show moderate to good agreement for most arm movements and scapular rotations. Thus, there exists distinct optimal configurations of non-invasive marker locations for accurately measuring scapular kinematics.

A new subject-specific skin correction factor for three-dimensional kinematic analysis of the scapula.

Noninvasive measurement of scapular kinematics using skin surface markers presents technical challenges due to the relative movement between the scapula and the overlying skin. The objectives of this study were to develop a noninvasive subject-specific skin correction factor that would enable a more accurate measurement of scapular kinematics and evaluate this new technique via comparison with a gold standard for scapular movement. Scapular kinematics were directly measured using bone pins instrumented with optoelectronic marker carriers in eight healthy volunteers while skin motion was measured simultaneously with optoelectronic markers attached to the skin surface overlying the scapula. The relative motion between the skin markers and the underlying scapula was estimated over a range of humeral orientations by palpating and digitizing bony landmarks on the scapula and then used to calculate correction factors that were weighted by humeral orientation. The scapular kinematics using these correction factors were compared with the kinematics measured via the bone pins during four arm movements in the volunteers: abduction, forward reaching, hand behind back, and horizontal adduction. The root-mean-square (rms) errors for the kinematics determined from skin markers without the skin correction factors ranged from 5.1 deg to 9.5 deg while the rms errors with the skin correction factors ranged from 1.4 deg to 3.0 deg. This technique appeared to perform well for different movements and could possibly be extended to other applications.

Three-dimensional rotation of the scapula during functional movements: an in vivo study in healthy volunteers.

The goal of this study was to measure 3-dimensional shoulder motion by use of a direct invasive technique during 4 different arm movements in healthy volunteers. Eight subjects with healthy shoulders were recruited. Optoelectronic marker carriers (ie, infrared light-emitting diodes) were mounted on bone pins, which were inserted into the lateral scapular spine. Subjects performed 4 different arm movements while the motion was being recorded by a precision optoelectronic camera. Joint angles were calculated in 3 dimensions. Intraclass correlation coefficients and root-mean-square differences were calculated as measures of reliability. During abduction, the scapula tipped posteriorly (44 degrees +/- 11 degrees), rotated upward (49 degrees +/- 7 degrees), and rotated externally (27 degrees +/- 11 degrees). For reaching, the scapula consistently rotated upward (17 degrees +/- 3 degrees) and rotated internally (18 degrees +/- 6 degrees) whereas tipping was generally less than 10 degrees (5 degrees +/- 2 degrees). Overall, the range of scapular movement for the hand behind the back was small and variable, with most rotations not exceeding 15 degrees. For horizontal adduction, the scapula tipped anteriorly (8 degrees +/- 3 degrees), rotated upward (5 degrees +/- 2 degrees), and rotated internally (27 degrees +/- 6 degrees). These scapular rotations provide normative data that will be useful for diagnosing scapular dysfunction.