Function of the posterior tibial tendon muscle.

The posterior tibial tendon muscle plays a critical role in the function of the foot. It is, with the exception of the triceps surae, the largest of the extrinsic foot muscles. It is called upon to provide a critical posturing and stabilizing function to the foot during gait. This review discusses the anatomy, physiology, functional characteristics, and measurement of the strength of this muscle.

A closed-loop cadaveric foot and ankle loading model.

Investigations of human foot and ankle biomechanics rely chiefly on cadaver experiments. The application of proper force magnitudes to the cadaver foot and ankle is essential to obtain valid biomechanical data. Data for external ground reaction forces are readily available from human motion analysis. However, determining appropriate forces for extrinsic foot and ankle muscles is more problematic. A common approach is the estimation of forces from muscle physiological cross-sectional areas and electromyographic data. We have developed a novel approach for loading the Achilles and posterior tibialis tendons that does not prescribe predetermined muscle forces. For our loading model, these muscle forces are determined experimentally using independent plantarflexion and inversion angle feedback control. The independent (input) parameters -- calcaneus plantarflexion, calcaneus inversion, ground reaction forces, and peroneus forces -- are specified. The dependent (output) parameters -- Achilles force, posterior tibialis force, joint motion, and spring ligament strain -- are functions of the independent parameters and the kinematics of the foot and ankle. We have investigated the performance of our model for a single, clinically relevant event during the gait cycle. The instantaneous external forces and foot orientation determined from human subjects in a motion analysis laboratory were simulated in vitro using closed-loop feedback control. Compared to muscle force estimates based on physiological cross-sectional area data and EMG activity at 40% of the gait cycle, the posterior tibialis force and Achilles force required when using position feedback control were greater.

Gait characteristics of patients after proximal femoral replacement for malignant bone tumour.

We analysed the gait characteristics of 15 patients with prosthetic reconstruction of the proximal femur after resection of a malignant bone tumour using stride analysis and measurement of oxygen consumption. Compared with normal volunteers their gait was slower, with less cadence and reduced stride length. The mean net energy cost of free walking was 141% of normal. The degree of asymmetry of the single-limb support time correlated with the free-walking velocity and the net energy cost. If they used a single cane the subjects walked with less cadence, longer stride length, and prolonged single-limb support times. The net energy cost of walking and asymmetry of the single-limb support time had a negative correlation with the strength of the hip abductor muscles. Their walking performance was better than that of six subjects who had hip disarticulation.

Deltoid ligament strain after correction of acquired flatfoot deformity by triple arthrodesis.

Deltoid insufficiency represents a difficult surgical challenge. We have witnessed patients who have developed a valgus tibiotalar deformity following a properly positioned triple arthrodesis. To investigate whether the triple arthrodesis itself, by creating a rigid triple joint complex below the ankle, leads to increased strain of the deltoid complex, a flatfoot model was created in 8 fresh-frozen below-knee amputation specimens. Each specimen was loaded in three gait cycle (GC) positions: Heel strike (0% GC), midstance (10% GC), and heel rise (40% GC). The three components of the ground reaction force (GRF) and the tendon forces consistent with those respective positions were applied. To simulate a posterior tibial tendon insufficient state the posterior tibial tendon was not loaded. Strain at the tibiocalcaneal fibers of the superficial deltoid ligament complex was determined at each of the three foot positions. A triple arthrodesis was performed and the deltoid strains were again recorded for each position. A significant increase in the strain of the deltoid ligament was observed for only the heel rise position (p=0.007) in our cadaver model following triple arthrodesis. The results favor medializing the calcaneus following arthrodesis to protect the deltoid complex.

Medial arch strain after lateral column lengthening: an in vitro study.

Posterior tibial tendon dysfunction with concomitant progressive flatfoot deformity is associated with ligamentous failure along the medial arch. Lateral column lengthening is being used alone and in combination with other procedures with the expectation that it contributes to restoring and maintaining the arch. The primary objective of this study was to examine the effect of lateral column lengthening on medial arch strain. A secondary objective was to examine the effect of subtalar, talonavicular, double and triple fusions on medial arch strain. Whole cadaver feet were subjected to vertical loads while in a plantigrade position. Spring ligament length was monitored using liquid metal displacement gauges. Two outcomes were examined: the length of the ligament and the change in length of the ligament per unit of applied load. Ligament length was unchanged after lateral column lengthening. Ligament length was decreased after talonavicular, double and triple arthrodeses, consistent with the ligament being protected by these fusions. The change in length per unit of applied load after simulated lateral column lengthening was comparable to that for the intact foot, which is consistent with the ligament remaining functional during weightbearing and not being overloaded.

Bootstrap prediction and confidence bands: a superior statistical method for analysis of gait data.

Gait analysis studies typically utilize continuous curves of data measured over the gait cycle, or a portion of the gait cycle. Statistical methods which are appropriate for use in studies involving a single point of data are not adequate for analysis of continuous curves of data. This paper determines the operating characteristics for two methods of constructing statistical prediction and confidence bands. The methods are compared, and their performance is evaluated using cross-validation methodology with a data set of the sort commonly evaluated in gait analysis. The methods evaluated are the often-used point-by-point Gaussian theory intervals, and the simultaneous bootstrap intervals of Sutherland et al. The Development of Mature Walking, MacKeith Press, London, 1988 and Olshen et al. Ann. Statist. 17 (1989) 1419-40. The bootstrap bands are shown to provide appropriate coverage for continuous curve gait data (86% coverage for a targeted coverage of 90%). The Gaussian bands are shown to provide inadequate coverage (54% for a targeted coverage of 90%). The deficiency in the Gaussian method can lead to inaccurate conclusions in gait studies. Bootstrap prediction and confidence bands are advocated for use as a standard method for evaluating gait data curves because the method is non-parametric and maintains nominal coverage levels for entire curves of gait data.

Medial arch strain after medial displacement calcaneal osteotomy: an in vitro study.

Posterior tibial tendon dysfunction with concomitant progressive flatfoot deformity is associated with ligamentous failure along the medial arch. Medial displacement calcaneal osteotomy is being used alone and in combination with other procedures, with the expectation that it contributes to maintaining the arch. The objective of this study was to examine the effect of osteotomy on reducing medial arch strain. Whole cadaver feet were subjected to vertical loads while plantigrade. Spring ligament length was monitored using liquid metal displacement gauges. Two outcomes were examined: the length of the ligament under one-half body weight and the change in length of the ligament per unit of applied load. The medial displacement calcaneal osteotomy allowed elongation of the ligament with weightbearing, but at a shorter ligament length. This afforded the spring ligament protection from the levels of force experienced in the intact and lateral column-lengthened conditions.

Radiographic evaluation of glenohumeral kinematics: a muscle fatigue model.

The purpose of this study was to document the effect of muscle fatigue on glenohumeral kinematics. Twelve male volunteers without shoulder disease and with an average age of 27 years were studied. Glenohumeral anteroposterior radiographs were taken at 45 degrees intervals as the arm was abducted in the plane of the scapula from 0 degree to 135 degrees. This series of radiographs was performed both before and immediately after the subject performed a series of deltoid and rotator cuff fatiguing exercises. The average humeral head position or translation before and after muscle fatigue for each arm angle was compared. For all subjects, before fatigue, the position of the humeral head was below the center of the glenoid for all angles of abduction. There was essentially no change in position of the humeral head in the prefatigue state, as the arm was abducted from 0 degree to 135 degrees with no more than an average 0.3 mm of total humeral head excursion. After fatigue, excursion of the humeral head increased to an average of 2.5 mm between the tested positions. The position of the humeral head with the arm at 0 degree of abduction was lower or had migrated inferiorly compared with the rested state, with an average 1.2 mm significant increase in inferior translation. With the initiation of abduction, the humeral head demonstrated significant superior migration or translation in all positions tested. This result has important implications for conservative treatment of shoulder impingement and underscores the importance of rehabilitation to maximize the endurance and strength of the rotator cuff musculature.

Interrelationships of clinical outcome, length of resection, and energy cost of walking after prosthetic knee replacement following resection of a malignant tumor of the distal aspect of the femur.

The relationships between the functional score according to the system of the International Society of Limb Salvage, the extent of resection, energy cost of walking, and gait characteristics were studied in thirty-six patients who had had segmental knee replacement after resection of a malignant tumor of the distal aspect of the femur. The mean free-walking velocity was 62.3 meters per minute (79 per cent of normal), which was a result of decreases in both cadence and stride length. The mean net energy cost during walking was 35 per cent greater than that of normal controls and correlated with the percentage of the femur that had been resected. All patients had decreased single-limb support time on the affected side compared with the unaffected side. There was a weak correlation between the asymmetry of the single-limb support time and the percentage of the femur that had been resected. The mean extensor torque of the affected knee was 30 per cent that of the unaffected knee when one head of the quadriceps muscle had been excised, 19 per cent when two heads had been excised, 4 per cent when three heads had been excised, and 1 per cent when four heads had been excised. The patients who had had an extra-articular resection had lower mean extensor and flexor torques at the knee compared with those who had had an intra-articular resection. The asymmetry of the single-limb support time was inversely related to the residual extensor and flexor torques. The overall score according to the system of the International Society of Limb Salvage ranged from 17 to 29 points (mean, 24.6 points; 82 per cent of normal). The net energy cost, percentage of maximum aerobic capacity, and asymmetry of the single-limb support time had significant negative correlations with the overall functional score. Multivariate analysis showed that the overall functional score and the percentage of the femur that had been resected were the two most important factors that predicted the net energy cost. To our knowledge, this is the first objective validation of the functional score according to the system of the International Society of Limb Salvage. As the net energy cost can be predicted from universally available, inexpensive measures, investigators can easily use it as a clinical and research tool to evaluate prosthetic performance and to assess operative outcome.

Prosthetic knee replacement after resection of a malignant tumor of the distal part of the femur. Medium to long-term results.

We evaluated the medium to long-term results of treatment with a custom prosthetic knee replacement after wide resection of a primary malignant tumor of the distal part of the femur in forty consecutive patients. The duration of follow-up ranged from five to seventeen years (median, eight years). At the time of the latest follow-up, thirty-five (88 per cent) of the forty patients were free of disease and five (13 per cent) were alive with metastatic disease. No local recurrence was observed. Twenty early complications occurred in eighteen patients (45 per cent). Aseptic loosening of the femoral component, which necessitated a revision in eleven patients at an average of fifty-one months, was the most frequent mode of failure. The rate of prosthetic survival, as estimated with use of the Kaplan-Meier method, was 85, 67, and 48 per cent at three, five, and ten years. Univariate analysis demonstrated that the rate of prosthetic survival was significantly worse for male patients, for those in whom at least 40 per cent of the femur had been resected, for those who had had total resection of the quadriceps muscles or subtotal resection (preservation of only the rectus femoris muscle), and for those in whom a straight femoral stem had been used (p < 0.05 for all comparisons). Multivariate analysis showed that the independent adverse prognostic factors for prosthetic survival were male gender, resection of at least 40 per cent of the femur, and fixation of the femoral stem with cement. The rate of limb salvage was calculated, with use of the Kaplan-Meier method, to be 93 per cent at three years and 90 per cent at five and ten years. At the latest follow-up examination, the functional scores according to the classification system of the Musculoskeletal Tumor Society ranged from 14 to 29 points; the mean was 24 points, which represents function that is 80 per cent that of normal. The mean scores in the categories of walking supports and gait were better for the patients in whom the quadriceps muscles had been preserved than for those who had had total or subtotal resection of those muscles. Although advances in imaging and local therapy narrow the indications for an extra-articular resection of a tumor, the implant that was used in the present study continues to be used in approximately 15 per cent of patients who have a fracture or an intra-articular extension of the tumor that necessitates extensive extra-articular resection.

Motion of the hindfoot after simulated arthrodesis.

Arthrodesis of the subtalar joint, triple arthrodesis (involving the subtalar, talonavicular, and calcaneocuboid joints), double arthrodesis (involving the talonavicular and calcaneocuboid joints), arthrodesis of the talonavicular joint, and arthrodesis of the calcaneocuboid joint were simulated in a cadaver model, and the range of motion of each joint not involved in the simulated arthrodesis was measured with a three-dimensional magnetic space tracking system. The excursion of the posterior tibial tendon was also measured under all of these conditions. We found that any combination of simulated arthrodeses that included the talonavicular joint severely limited the motion of the remaining joints to about 2 degrees and limited the excursion of the posterior tibial tendon to 25 per cent of the preoperative value. Simulated arthrodesis of the calcaneocuboid joint had little effect on the range of motion of the subtalar joint, and it reduced the range of motion of the talonavicular joint to a mean of 67 per cent of the preoperative value; a mean of 73 per cent of the excursion of the posterior tibial tendon was retained. After simulated arthrodesis of the subtalar joint, a mean of 26 per cent of the motion of the talonavicular joint, 56 per cent of the motion of the calcaneocuboid joint, and 46 per cent of the excursion of the posterior tibial tendon was retained. The talonavicular joint is the key joint of the triple joint complex. The talonavicular joint had the greatest range of motion, and simulated arthrodesis of this joint essentially eliminated motion of the other joints of the complex.

Radiologic measurement of superior displacement of the humeral head in the impingement syndrome.

A method for directly measuring the position of the humeral head on the face of the glenoid in different positions of abduction of the arm was developed. We studied three subject groups: 12 patients with normal shoulders (group 1), 15 patients with stage II impingement syndrome (group 2), and 20 patients with rotator cuff tears or stage III impingement (group 3). The study consisted of a series of anteroposterior roentgenograms in the plane of the scapula with the arm in neutral rotation. Roentgenograms were obtained at 20 degrees intervals as the arm was elevated in the plane of the scapula from 0 degree to 120 degrees. Patients held a weight equal to 2 1/2% of body weight in the hand. The parameters measured were excursion of the humeral head on the glenoid face, expressed as the distance that the center of the head lies above or below the center of the glenoid, arm angle, scapulothoracic angle, and glenohumeral angle. For patients with normal shoulders (group 1), there was no significant change in position of the humeral head with arm elevation. In contrast, those with stage II impingement (group 2) had significant (p < 0.05) superior displacement of the center of the humeral head with arm elevation. Patients with rotator cuff tears (group 3) demonstrated a significant rise (p < 0.05) during the first 40 degrees of abduction. The average position of the humeral head in the two pathologic patient groups was superior (p < 0.05) to the average head position in the normal patient group. There was no significant difference in head position between patients with stage II impingement and patients with rotator cuff tear. The ratio of the glenohumeral angle to the scapulothoracic angle during abduction was calculated for our patient groups. In both patient groups, arm abduction had a larger scapulothoracic component than for normal shoulders. The superior migration of the humeral head is a probable result of cuff failure, either partial or complete.

Lateral column lengthening with calcaneocuboid fusion: range of motion in the triple joint complex.

Lengthening the lateral column of the foot has been shown to correct flatfoot deformity. In adults, however, lengthening leads to calcaneocuboid arthritis. Lateral column lengthening with calcaneocuboid fusion, which lengthens the lateral column of the foot and prevents calcaneocuboid arthritis, was investigated in a cadaver model to determine the remaining range of motion in the talonavicular and subtalar joints. Inversion/eversion motion was produced by tendon pulls and the range of motion was measured in three dimensions using a magnetic space tracker. After lateral column lengthening with calcaneocuboid fusion, 48% of talonavicular and 70% of subtalar joint range of motion were preserved. Analysis of the inversion and eversion ranges of motion suggests that the lengthening fusion limits eversion more than inversion. These findings demonstrate the need for clinical investigation of this procedure, which could preserve motion in the talonavicular and subtalar joints, correct deformity, and obviate calcaneocuboid arthritis.

A custom distal femoral prosthesis for reconstruction of large defects following wide excision for sarcoma: results and prognostic factors.

Between 1979 and 1986, 37 patients with sarcoma of the distal femur underwent limb salvage using a custom prosthetic knee replacement. Thirteen (35%) had early complications. Fourteen (38%) had late complications, which consisted of 6 aseptic femoral loosenings, 1 aseptic tibial loosening, 2 tibial fractures, 2 contractures, 1 femoral fracture, 1 prosthetic fracture, and 1 septic loosening. By 1988, nine patients died. Thirteen prostheses failed in 12 patients, resulting in 9 revisions, 2 above-knee amputations, and 2 Van Nes rotationplasties. The 2- and 5-year prosthetic survival rates were 82% and 57%, respectively. Twenty-two of the 26 survivors (85%) had successful limb salvage. Preventable factors were implicated in the loosening of six femoral components and in one femoral fracture. The mean Hospital for Special Surgery Knee Score was 69 (range: 62 to 86).

Changes in the moment arms of the rotator cuff and deltoid muscles with abduction and rotation.

The behavior of the moment arms of the rotator cuff and deltoid muscles was studied during simple and combine movements of abduction and rotation about the glenohumeral joint. This was done by experimental measurement of excursions of the muscles in an in vitro cadaver model and by use of a multiple-regression analysis to delineate the changes in the moment arms as a function of abduction and rotation. The results demonstrated the potential of some rotator cuff muscles to contribute to both abduction and rotation, the sensitivity of the abductor moment-arm lengths to internal and external rotation and of the rotator moment-arm lengths to the degree of abduction, and the capacity of the abductor moment-arm lengths of the deltoid to increase with increasing abduction. Characterization of this behavior resulted in an increased understanding of the complex role of the rotator cuff and deltoid muscles about the gleno-humeral joint and provided quantitative descriptions of functional relationships. This study demonstrates the capacity of the infraspinatus and subscapularis muscles to contribute not only to external and internal rotation, respectively, but also to elevation of the arm in the plane of the scapula, a role for which these muscles have been given little or no consideration. Furthermore, it demonstrates that the contribution of the infraspinatus to abduction is enhanced with internal rotation while that of the subscapularis is enhanced with external rotation. Thus, dysfunction of the supraspinatus muscle need not preclude good elevation of the arm, and rehabilitation to reprogram and strengthen the remaining muscles becomes an important consideration.

The effects of sectioning of the posterior cruciate ligament and the posterolateral complex on the articular contact pressures within the knee.

Articular contact pressures in ten cadaveric knees with intact ligaments were measured with the use of film and a model that simulated non-weight-bearing resistive extension of the knee. The measurements were repeated after sequential sectioning of the posterior cruciate ligament and the posterolateral complex (the posterolateral capsule, the popliteus muscle and tendon, and the lateral collateral ligament). Patellofemoral pressures and quadriceps load were most significantly elevated after combined sectioning of the posterior cruciate ligament and the posterolateral complex. Medial compartment pressure was significantly elevated after sectioning of the posterior cruciate ligament. The results coincided with, and may partially explain, the clinical findings associated with these types of ligamentous injuries.

Effect of a walking program on gait characteristics in patients with osteoarthritis.

This paper reports the results of a study of the gait of 102 patients with osteoarthritis of the knee. Functional status was measured by a 6-min test of walking distance; the stride characteristics associated with the walk test were assessed. Stride characteristics were measured by a Stride Analyzer. Patients were randomized to an 8-week educational and walking program (the intervention group) or to a weekly telephone survey (the control group). The intervention group patients had a 15% increase in walking distance (P < 0.0001) and increases of 9.1% in stride length at free walking speeds (P < 0.007) and 17% in stride length at fast walking speeds (P < 0.01) compared to the control group. The results of this study have shown that the walking and educational program was effective in improving gait function in patients with osteoarthritis of the knee.

Prosthetic arthroplasty of the knee after resection of a sarcoma in the proximal end of the tibia. A report of sixteen cases.

The results of a specific type of prosthetic reconstruction of the knee (total replacement arthroplasty) after resection of a sarcoma of the proximal part of the tibia in sixteen patients were retrospectively reviewed. The diagnosis was stage-IIB osteogenic sarcoma in nine patients, stage-IIB malignant fibrous histiocytoma in three patients, and stage-IB sarcoma of various types in four patients. The length of tibial resection ranged from 100 to 257 millimeters. Of the eleven patients who were available for functional examination (mean duration of follow-up, sixty-three months), three patients had an excellent result, seven had a good result, and one had a fair result. Of the five patients who were not available for functional testing, one who was doing well was lost to follow-up at eighty months, one had died of metastases at sixteen months, and three had had a secondary amputation for infection or for loosening of the prosthesis.

The Van Nes tibial rotationplasty. A functionally viable reconstructive procedure in children who have a tumor of the distal end of the femur.

Twelve patients who had a malignant tumor of the distal end of the femur were treated with a Van Nes tibial rotationplasty. The survival rates were comparable with those for above-the-knee amputees and patients who had an endoprosthetic replacement. The results of functional testing showed that these patients performed as well as those who had endoprosthetic replacement and better than those who had above-the-knee amputation. Rotationplasty is therefore a favorable alternative to amputation or endoprosthetic replacement, either as a primary or as a salvage procedure.