Hind- and Midfoot Motion After Ankle Arthrodesis.

BACKGROUND: After ankle arthrodesis (AA), compensatory increased range of motion in adjacent joints might lead to increased osteoarthritis. Evaluation of patient-reported outcomes after AA with validated questionnaires is rare. Likewise, reliable radiographic analysis of the position of the AA, expected to influence the range of motion of the hind- and midfoot, is lacking. Therefore, the current study was performed. METHODS: Seventeen patients with unilateral AA were included. Sagittal hind- and midfoot range of motion was measured radiographically. The position of the AA in the sagittal and coronal planes and osteoarthritis of adjacent joints were also evaluated radiographically. Measurements were compared to the contralateral side. Patient-reported outcomes via validated questionnaires were compared to a control group (n = 18). RESULTS: Average follow-up was 3.5 years. Mean combined hind- and midfoot sagittal range of motion after AA equaled that of the contralateral side (20.8 vs. 21.0 degrees; P = .93). The tibiotalar angle after AA equaled that of the contralateral side (107 vs. 107 degrees; P = .86). The talus was translated posteriorly after AA (T-T ratio 0.45 vs. 0.34; P < .001). Low intraclass correlation coefficients (ICC) precluded reliable evaluation of the coronal position of the hindfoot (ICC, 0.07 and -0.34) and osteoarthritis in adjacent joints (ICC range, 0-0.54). SF-36 physical health scores after AA are lower as compared with those of controls (50 vs. 56; P = .01). Scores on the Foot and Ankle Outcome Score and Ankle Osteoarthritis Scale were also significantly lower. Patient satisfaction with AA was high (average visual analog scale score, 83). CONCLUSION: No increased sagittal range of motion in the hind- and midfoot after AA was found at 3.5 years of follow-up as compared with the contralateral side. Tibiotalar angles were equal. The talus was translated posteriorly. The hindfoot alignment view was not suitable to analyze the position of the hindfoot. Low ICC of the Kellgren and Lawrence scale precluded evaluation of osteoarthritis of adjacent joints. Patients scored lower than controls on self-reported outcome questionnaires but were satisfied with the result of AA.

The effect of neighboring segments on the measurement of segmental stiffness in the intact lumbar spine.

BACKGROUND CONTEXT: Degeneration, injury, and surgical interventions may alter the mechanical properties of spinal motion segments, but the quantification of these alterations in vivo is problematic. Manual or instrumented loading of single segments in the intact spine as applied intraoperatively may overestimate the mechanical properties of this segment, because the applied load is partly sustained by the adjacent segments. PURPOSE: The distribution of stiffness values of individual spinal segments within and across spines was determined so as to use these data as input to a model simulation of segment stiffness tests in intact spines, to assess measurement errors. STUDY DESIGN: Biomechanical stiffness measurements on human cadaveric spines and model simulation to assess measurement errors. METHODS: Seventeen human cadaveric lumbar spines were loaded with pure moments in flexion/extension, lateral bending, and torsion. An optical system was used to measure the angular rotations of each motion segment and load-displacement curves were used to determine stiffness. With the distribution of measured stiffness data as input, a stochastic mechanical model was constructed to investigate how the stiffness of adjacent segments influences stiffness estimates obtained by loading a single segment in the intact spine. RESULTS: The variance in stiffness values was high for all directions, but covaried between segments within a spine. Model simulations indicated that stiffness estimates obtained by loading a single segment in an intact spine are highly correlated with actual stiffness, but overestimate stiffness by a median of 18% with peak errors of close to 400%. CONCLUSION: Current measurement devices and manual assessment substantially overestimate segmental stiffness due to the effect of adjacent spinal levels. In addition, the variance in stiffness within spines can occasionally cause large errors, which might lead to erroneous surgical decisions.

Single level lumbar laminectomy alters segmental biomechanical behavior without affecting adjacent segments.

BACKGROUND: Degenerative lumbar spinal stenosis causes neurological symptoms due to neural compression. Lumbar laminectomy is a commonly used treatment for symptomatic degenerative spinal stenosis. However, it is unknown if and to what extent single level laminectomy affects the range of motion and stiffness of treated and adjacent segments. An increase in range of motion and a decrease in stiffness are possible predictors of post-operative spondylolisthesis or spinal failure. METHODS: Twelve cadaveric human lumbar spines were obtained. After preloading, spines were tested in flexion-extension, lateral bending, and axial rotation. Subsequently, single level lumbar laminectomy analogous to clinical practice was performed at level lumbar 2 or 4. Thereafter, load-deformation tests were repeated. The range of motion and stiffness of treated and adjacent segments were calculated before and after laminectomy. Untreated segments were used as control group. Effects of laminectomy on stiffness and range of motion were tested, separately for treated, adjacent and control segments, using repeated measures analysis of variance. FINDINGS: Range of motion at the level of laminectomy increased significantly for flexion and extension (7.3%), lateral bending (7.5%), and axial rotation (12.2%). Range of motion of adjacent segments was only significantly affected in lateral bending (-7.7%). Stiffness was not affected by laminectomy. INTERPRETATION: The increase in range of motion of 7-12% does not seem to indicate the use of additional instrumentation to stabilize the lumbar spine. If instrumentation is still considered in a patient, its primary focus should be on re-stabilizing only the treated segment level.