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Limb lengthening in the left tibia of 30 mature female Yucatan micropigs was performed using distraction osteogenesis. A treatment group of 15 animals received recombinant porcine growth hormone (r-pGH) (100 microg/kg/day) while the others served as controls. Serial serum measurements of total insulin-like growth factor I (IGF-I), free IGF-I, IGF binding proteins -1, -2, -3 and -4 (IGFBP-1 to -4) were performed. Bone-specific alkaline phosphatase (bone-ALP) and the serum carboxyl-terminal telopeptide of type I collagen (ICTP) were measured as bone turnover markers. The GH-treated animals showed a significant increase in total IGF-I, free IGF-I and IGFBP-3 after surgery (P<0.001). Similarly, the treated animals showed a significantly higher level of bone-ALP (P<0.001) throughout the experiment compared to the controls. There was a significant correlation between bone-ALP and total IGF-I (r=0.76) in the GH-treated group and an even higher correlation for free IGF-I (r=0.90). There was no difference in the ICTP serum levels between the two groups. These data indicate that the application of species-specific growth hormone results in a stimulation of bone formation in distraction osteogenesis which may be mediated by IGF-I. The stronger correlation between free IGF-I and bone-ALP indicates that the anabolic effect of IGF-I may be regulated through the IGFBPs by binding and inactivating IGF-I., (Copyright 2001 Harcourt Publishers Ltd.)

Modern shoulder prostheses permit an anatomic reconstruction of the joint, although the biomechanical advantages are not proven. The goal of this study was to investigate the relationship between position of the humeral head and function of the shoulder prosthesis (muscle efficiency). Shoulder elevation-motion and rotator cuff defects were simulated in vitro in a robot-assisted shoulder simulator. The EPOCA Custom Offset shoulder prosthesis (Argomedical AG, Cham, CH) was implanted in seven normal shoulders (77 +/- 20 kg, 55 +/- 14 years). Active elevation was simulated by hydraulic cylinders, and scapulothoratic motion by a specially programmed industrial robot. Muscle efficiency (elevation-angle/muscle-force of the deltoid muscle) was measured in anatomic (ANA), medialised (MED) and lateralised (LAT) positions of the humeral head, with or without rotator cuff muscle deficiency. Medialisation increased efficiency by 0.03 +/- 0.04 deg/N (p = 0.022), lateralisation decreased it by 0.04 +/- 0.06 deg/N (p = 0.009). Supraspinatus muscle deficiency increased the deltoid force required to elevate the arm, and thus decreased efficiency (ANA p = 0.091, MED p = 0.018, LAT p = 0.028). The data confirm that the position of the humeral head affects the mechanics of total shoulder arthroplasty. Medialisation increases efficiency of the deltoid muscle and may prove useful in compensating isolated supraspinatus muscle deficiency. Lateralisation, in contrast, leads to an unfavorable situation.

The effect of a medially based anterior capsular shift on translational and rotational range of motion and posterior capsular strain was investigated in an in vitro model. Six cadaveric shoulders were tested in a robot-assisted shoulder simulator. Translational and rotational range of motion were reduced by the capsular shift, particularly with the shoulder at higher elevation angles. At 60 degrees of elevation, anterior translation was decreased 1.9 +/- 2.9 mm, and posterior translation was decreased 2.3 +/- 6.2 mm. External rotation was decreased 11.5 degrees +/- 10.2 degrees, and internal rotation was decreased 8.9 degrees + 5.7 degrees. Posterior capsular strain change was dependent on elevation angle. At 30 degrees of elevation, strain tended to increase 5.0% +/- 7.3% in the inferior aspect and 2.9% +/- 2.6% in the superior aspect, with no change detected in the medial aspect. At 60 degrees of elevation, strain increased 6.6% +/- 8.0%, 3.2% +/- 2.6%, and 4.4% +/- 3.5% in the inferior, middle, and superior aspects, respectively. Our results support the use of the medially based anterior shift for shoulders with anterior-inferior instability or multidirectional instability with posterior involvement.

The present article describes a newly developed device for the quantitative assessment of torsional in vivo stiffness of regenerating bone under callus distraction. Both the design and function of this device, and its use during bony consolidation are discussed. The device exhibited an accuracy of +/- 18% for stiffness under 0.1 Nm/degree, and +/- 5% stiffness above 0.1 Nm/degree. The average accuracy was +/- 14%. The data scatter for the stiffness measurement ranged between +/- 1.43% and +/- 7.68% (average: +/- 3.99%). The precision of a test machine was between +/- 0.01% and +/- 11.3% (average: +/- 3.65%). The method has the following advantages over existing methods for investigating healing: 1. no need to dismantle the external fixation for measurement; 2. preservation of the bone axis with minimal risk of misalignment during the bone healing process; 3. minimal technical requirements, with easy, noninvasive measurement; 4. no exposure to X-radiation.

We present a new method for quantitatively assessing the consolidation of bone regeneration by performing distraction osteogenesis in micropigs. We measured in vivo stiffness using a newly developed, revolving, bone-healing meter. After the micropigs were killed, we obtained maximum torsional moment data for the regenerated bones by destructive mechanical testing, and we then correlated these data with the data for stiffness. We found a highly significant regression between in vivo stiffness and maximum torsional moment (r2 = 0.80), suggesting that monitoring stiffness may be useful for the prediction of bone regeneration in distraction osteogenesis. Therefore, our method may be a reliable tool for future quantitative monitoring of healing progress in patients with healing bones or in animal studies addressing treatments to increase bone formation in long-bone defects.

Study Design: Structural properties of vertebrae with simulated defects were measured from computed tomography data. Relations between structural properties and postfracture stability were tested using linear regressions., Objectives: To determine whether the postfracture stability of lumbar and thoracic vertebrae can be predicted from noninvasive, prefracture measurements of structural properties., Summary of Background Data: Sensitive and specific guidelines are needed that can predict fracture risk and spinal stability after pathologic fractures. Such guidelines may help determine whether treatment is needed to prevent neurologic complications. Simple measurements made from computed tomography data can predict the load-bearing capacity of intact vertebrae and vertebrae with simulated and actual metastatic defects. It is not known whether these same measurements can also predict postfracture stability., Method: Simulated metastatic defects were created in human three-vertebrae segments from the lumbar and thoracic spine. Axial rigidity was calculated from quantitative computed tomography data, and failure load and postfracture stability were measured., Results: Postfracture stability was linearly correlated with both failure load (r2 = 0.3-0.6) and axial rigidity (r2 = 0.3-0.6)., Conclusions: The postfracture stability of three-vertebrae segments with simulated defects was modestly related to noninvasively measured, prefracture structural properties.

The newly formed regenerate bone during limb lengthening usually is assessed by observing standard plain radiographs. However, no objective data correlate the radiographic appearance with the quantitative strength of the newly formed bone. A noninvasive method was developed to assess the regenerate bone using digital radiography. The investigations were performed in a micropig animal model. The right tibia was distracted for 10 days at 2 mm per day. Digital radiography was performed after the distraction during a 10-day consolidation period. For quantitative analysis, an aluminum step wedge was placed on all images, and a region of interest was outlined in the regenerate bone. A calibration curve was calculated by measuring the corresponding gray values of the aluminum phantom. The calibration equation was used for determining the mean density in the region of interest. This method was sensitive in assessing day to day healing progress. The measurements taken the day before sacrifice were compared with torsional mechanical data using a material testing machine. The high correlation between the densimetric evaluations and the biomechanical data suggests this method is a useful tool for in vivo assessment of the regenerate bone during the consolidation period in distraction osteogenesis.

We present a newly developed torsional stiffness measurement device with the potential to quantitatively assess the in vivo torsional stiffness of bone regenerate during distraction osteogenesis. We describe the form and function of this device and its application in a model of regenerate consolidation. The device was able to produce data to assess stiffness of the regenerate with an accuracy between +/- 3 and +/- 9% for material stiffness ranging between 0.1 and 2.4 Nm/o and with a precision of +/- 3.6%. This method provides advantages over similar methods of bone fracture healing assessment with guaranteed maintenance of bone axis, minimized risk of bone misalignment during the bone healing process and a close relation to the functional loading pattern in torsion of bones such as tibia and femora.

The purpose of the present study was to prove whether homologous GH has a stimulating effect on bone healing. Therefore, left tibiae of 30 micropigs were osteomized and distracted over an external fixator at the rate of 2 mm/day on each of 10 consecutive days. Animals were killed after a healing period of another 10 days. The treatment group received 100 microg of recombinant porcine growth hormone (rpGH) per kilogram of body weight per day. Serial torsional nondestructive biomechanical tests were performed in vivo using a newly developed measurement device. After killing, destructive torsional strength testing of the sites of distraction was performed. To determine the endocrine response to the administration of rpGH, serum levels of insulin-like growth factor-I (IGF-I) were determined. Nondestructive in vivo testing showed that torsional stiffness of the regenerate was significantly higher in the treatment group than in the control group. Final regenerate torsional failure load was 131% higher and ultimate torsional stiffness was 231% higher in the treatment group than in the control group. The mean serum level of IGF-I increased to 440% of preoperative basal level in the treatment group and remained unchanged in the control group. Our data indicate that systemic administration of recombinant homologous growth hormone greatly accelerates ossification of bone regenerate in distraction osteogenesis.

Recently, increased interest in biodegradable interference screws for bone-tendon-bone graft fixation has led to numerous screws becoming available. The implants are made from different polymers and have different designs, which might influence their mechanical properties. Several studies have reported a wide range of mechanical results for these screws using different biomechanical models. The aim of the present study is to compare reliable biomechanical data for six different biodegradable interference screws, consisting of five different polymers, with a conventional titanium screw in a standardized model. Seventy proximal calf tibias were used to determine maximal pull-out force, stiffness of fixation, and insertion torque for interference screw fixation of bone-tendon-bone grafts. Additionally, maximal torque at failure was determined. Data were analyzed with respect to aspects of screw design, such as drive and thread shape. Five of the six biodegradable screws provided initial pull-out force and stiffness of fixation comparable with that of a conventional titanium screw. Torque at failure can be greatly increased by adapting the drive design to the mechanical properties of the polymeric raw material. A correlation between pull-out force and thread height indicates that fixation rigidity depends on screw design, even in a biodegradable implant.

Indications for operative treatment in spinal metastatic disease depend on estimates of vertebral loadbearing capacity. There are no noninvasive diagnostic tools for estimating vertebral loadbearing capacity in the presence of a metastatic lesion. Thus, relationships between vertebral failure load and measurements from computed tomography data were investigated to determine if measurements that account for defect size and bone density can predict loadbearing capacity better than can defect size alone. Cylindrical defects were created in thoracic vertebrae of 20 anatomic specimen spinal segments, with 10 other segments serving as controls. Five vertebrae with actual metastatic defects also were tested. Vertebrae were scanned using quantitative computed tomography, and the defect size and the axial rigidity of the midvertebral cross section were calculated using an image analysis program. The spinal segments were tested to failure using a combination of axial compression and anterior flexion. Linear regressions between axial rigidity and absolute failure load showed a high positive correlation, but there was no correlation between defect size and failure load. Axial rigidity may prove useful as a noninvasive assessment of vertebral loadbearing capacity in patients with spinal metastatic disease.

Recent operative techniques with percutaneous screw fixation of the tibial plateau require a high level of patient compliance. Geriatric, non-cooperative patients and fractures with severe soft tissue injury have had to be excluded so far from this therapeutic regimen. Since September 1993, composite hybrid fixation, as a combination of ring fixation of the epimetaphyseal tibia with monolateral AO fixation of the tibial shaft, has been performed in 12 patients. The data were collected prospectively. Fractures were classified according to the AO and Moore classification; soft tissue damage was classified according to Tscherne and Gustilio. Fixation was performed with the cannulated AO system, 2.0 mm titanium K wires and 5.0 mm AO Schanz screws. In five patients, additional arthroscopic control of the reposition was performed. Average removal of the external fixator was 16 weeks postoperatively. Pin-tract infections occurred in all patients, mainly in the metaphyseal region. In one patient, a knee infection resulted from a subchondral intra-articular pin, which was treated by repetitive arthroscopic synovectomy. In two patients, a secondary loss of reposition (5-7 degrees varus) occurred. Despite a high rate of soft tissue damage (8/12), no osteitis or non-union occurred. As an alternative to extensive methods of ORIF, supportive composite hybrid fixation offers a new perspective of early functional treatment, weight bearing and a rare loss of reposition. It is favored in geriatric, non-cooperative patients and in fractures with severe soft tissue damage.