Rollback in posterior cruciate ligament-retaining total knee arthroplasty. A radiographic analysis.

A clinical and radiographic study of 49 posterior cruciate ligament-retaining total knee arthroplasties in 38 patients (11 bilateral, 27 unilateral), using prostheses of the same design, was undertaken to quantify the amount of in vivo rollback (ie, the anteroposterior translation of the tibia with respect to the femur during flexion). The mean difference in the distances between the contact points of the knees in full extension and in 90 degrees flexion (ie, the rollback distance) was a posterior translation of the contact point of -0.2 mm (-12.7 to +7l6 mm; SD, 4.7 mm) relative to the prosthetic tibial tray, corresponding to an average translation of 0% of the prosthetic tibial tray depth, and -0.2 mm (-12.5 to +9.1 mm; SD, 4.8 mm) relative to the tibia itself, corresponding to an average translation of 0% of the true tibial surface depth. The differences between the rollback values obtained from the 90 degrees and full-extension radiographs relative to the prosthetic tibial tray (P = .63) and the true tibia (P = .89) were not statistically significant. Intraobserver (P = .27-.50) and interobserver (P = .13-.72) reliability tests showed that the differences between radiographic measurements taken by the same observer at two different points in time and by two different observers were not statistically significant. No correlations were found between the degree of translation of the tibiofemoral contact point relative to the prosthetic tibial tray and the posterior tilt of the tibial tray (R2 = .12), the preoperative tibiofemoral angle (R2 = .34), and the postoperative tibiofemoral angle (R2 = .027). No correlations were found between the degree of translation of the tibiofemoral contact point relative to the true tibia and the posterior tilt of the tibial tray (R2 = .16), the preoperative tibiofemoral angle (R2 = .14), and the postoperative tibiofemoral angle (R2 = .034). In conclusion, this study indicated no demonstrable rollback occurring in the posterior cruciate ligament-retaining total knee arthroplasty used in this study.

The Nicolas Andry Award-1995. Fracture healing. Radiation induced alterations.

This study investigated the effects of radiation on fractures in a rat femur model. Two different radiation dosage fractionation schemes (1100 rads given in one dose and 2500 rads given in 10 divided doses over 12 days) and three different times of initiation of radiation (1 day before fracture, 3 or 10 days after fracture) were studied. Fractures exposed to these levels of radiation all appeared to heal during the course of this experiment, although with varying degrees of delay, with the exception of those exposed to a single dose of 1100 rads 3 days after fracture. These animals remained at a more immature level of repair histologically compared with the control group, throughout the entire time evaluated. The strength of the final repair remained less than the control for all the groups receiving treatment. These results may offer some explanation for the clinical observations of an increased incidence of delayed union and nonunion of fractures, an increased incidence of fracture and refracture in irradiated bone, and an increased incidence of fracture and nonunion in constructs using radiation in conjunction with allogeneic bone. Furthermore, the observed effects were generally no different in the animals treated with the two clinically relevant dose fractionation schemes chosen for this study.

Effects of prefracture irradiation on the biomechanical parameters of fracture healing.

This study examined the effects on the biomechanical parameters of fracture healing of a single dose of 900 rad (the approximate single-dose equivalent of 2,500 rad in 10 divided doses), given 1 day prior to closed fracture of the femur. The femurs were recovered at 2, 3, 4, 8, and 16 weeks after fracture and were mounted and tested to failure in torsion; the results were compared with those in nonirradiated controls from a previously published study. Prefracture irradiation delayed the progressive increase in biomechanical parameters of fracture healing. The delay was statistically significant up to 8 weeks after fracture. At 4 weeks, the normalized torque was 44% that of intact bone in the treated group compared with 75% for the control group. Sixteen weeks after fracture, the biomechanical and histological parameters of fracture healing of the irradiated femurs were no different from those of the nonirradiated controls. Within the treated group, the irradiated fractures remained significantly weaker than their contralateral intact bone at all time intervals, with a torque of only 79% that of intact bone at 16 weeks. Thus, femoral fractures in rats healed (or regained substantial strength) following palliative doses of radiation delivered 1 day prior to injury, but the repair process was delayed compared with that of nonirradiated controls.

Posterior element strength six months postinjury in the canine cervical spine.

In vivo and in vitro biomechanical studies from this research group revealed that acute differences in the range of motion of C4-C5 canine cervical spine injuries decreased over a 24-week healing period to approach control values. It could be inferred that the repair tissue replacing the injured posterior elements functionally returned the spine to normal. This study investigated the biomechanical properties of the healed tissue and the isolated adjacent posterior elements at each intervertebral level of these same specimens. Twenty-two animals underwent one of four procedures at the C4-C5 level: (a) sham procedure, (b) transection of the supra- and interspinous ligament, (c) laminectomy, or (d) laminectomy plus bilateral facetectomy of the inferior articular facets. Twenty animals survived the entire testing protocol. Twenty-four weeks after injury, destructive testing was performed on the isolated posterior elements in tension loading. The maximum load, elongation at maximum load, stiffness, and energy absorbed to the maximum load were measured. The posterior elements injured by all of the procedures behaved similarly across all experimental groups after 24 weeks of healing. A trend for decreased stiffness in the more extensive surgery groups was seen, but no statistically significant differences were found. This paralleled the results of prior in vivo and in vitro range-of-motion testing.

Postfracture irradiation effects on the biomechanical and histologic parameters of fracture healing.

The effects of single-dose local irradiation on the biomechanical properties of closed femoral fractures were studied in 75 mature Sprague-Dawley rats. Ten days after fracture, the rats were irradiated with 900 rads at 250 kV to the entire fractured femur. At 2, 3, 4, 8, and 16 weeks after fracture, both fractured and contralateral intact femurs were recovered and evaluated biomechanically by testing to failure in torsion. Results were compared with those from a similar study involving fractures irradiated 3 days after fracture as well as nonirradiated control fractures. Fracture healing progressed faster when irradiation was delayed 10 days than when delayed 3 days, and control fractures healed more rapidly than after either delay. In the 10-day delay group, fractures showed greater strength than did those in the 3-day delay group at 8 weeks, but the strength of irradiated fractures in both groups was similarly depressed at 16 weeks, with a maximum torque well below that of control fractures. These results suggest that delaying radiation exposure of a fracture may mitigate short-term deleterious effects on fracture repair, but that long-term results may be similar to those associated with expeditious irradiation.

The noncemented porous-coated hip prosthesis. A three-year clinical follow-up study and roentgenographic analysis.

This was a retrospective study reviewing 68 hip arthroplasties performed with noncemented, porous-coated components at three institutions in the period between December 1983 and June 1987. Fifty of these were available for follow-up study. The mean follow-up period was three years (range, 18-56 months). Thirty-seven patients were treated by total hip arthroplasty (THA) with porous-coated components, and thirteen were implanted with porous-coated femoral stems with bipolar endoprostheses using a porous-coated femoral stem and a universal head. The mean Harris hip score at follow-up evaluation for the entire group was 85.7 points. Eighty percent of the patients had either a good or excellent result. Those patients implanted with a porous femoral stem with bipolar acetabular components had only 54% good or excellent results compared with 90% good or excellent results for those having THA. Roentgenographic findings included a 59% rate of femoral neck cortex osteopenia, an 80% rate of medial or lateral distal cortical hypertrophy, and an 80% rate of distal bone bridging. All of these roentgenographic changes were secondary to changes in stress transference to the proximal femur. There was no correlation between thigh pain or the degree of bone-prosthesis radiolucencies and the fit of the femoral stem.

The influence of ibuprofen on fracture repair: biomechanical, biochemical, histologic, and histomorphometric parameters in rats.

Ibuprofen is a widely used cyclo-oxygenase inhibitor in clinical practice. It has been demonstrated by others to have an inhibitory effect on fracture repair in animals. In the present study, we were unable to demonstrate any significant alterations in fracture biomechanics as measured by torsion testing and fracture stage in mature Sprague-Dawley rats treated with 30 mg/kg/day oral dose of ibuprofen, starting 3 days following fracture, over a 12-week time interval. Fracture histology and serum osteocalcin levels were no different in treated animals than control animals. Furthermore, histomorphometric parameters of bone remodeling, including bone volume and bone formation rate in the intact tail vertebrae of these animals with unilateral femur fractures, were no different between treated and control animals.

Cervical spine stabilization. A three-dimensional, biomechanical evaluation of rotational stability, strength, and failure mechanisms.

The three-dimensional rotational biomechanical properties of several different types of posterior stabilizing procedures are reported. A severe ligamentous and bony injury was simulated with three vertebral body human cervical spine segments. Good stabilization was noted for all of the repairs in flexion loading. Without polymethylmethacrylate supplementation, none of the repairs was stable in extension. All of the repairs provided reasonable stabilization for lateral bending except for the posterior wiring without methacrylate, and all but the posterior wiring and facet fusion provided reasonable stabilization against axial rotation loading. The supplementation of all of these repairs with polymethylmethacrylate added considerably to the stability of all the constraints. These findings may be useful in clinical decision-making for determining the kind of repairs and postoperative brace protection to use.

Functional stability of the canine cervical spine after injury. A three-month in vivo study.

Although clinical instability is an in vivo problem, most spinal instability criteria are either subjective or are based on in vitro experiments. The authors performed an in vivo experiment using a canine model to study the natural history of spinal instability as a function of healing time up to 12 weeks. Three injuries were produced surgically: sham; laminectomy at C4; and bilateral facetectomy at C4-C5. Three 1.5-mm steel balls were implanted into C3 to C6 vertebrae at the time of surgery. Standardized functional flexion-extension stereoradiographs of the cervical spine were obtained before injury, immediately after injury and at 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7.5, 9, and 12 weeks postinjury and immediately after killing the animals. In general, the authors found decreased ranges of motion (ROM) at the C4-C5 level, compared with the pre-injury values, for all injuries, but most significantly for the facetectomy. The maximum decrease occurred between 0 and 0.5 weeks postinjury. Between 2 and 12 weeks, there was recovery in the ROM, especially for the two less severe injuries. The changes in the ROM at each spinal level were explained by simultaneous presence of a destabilizing factor, caused by the three different injuries with the sham as the least and the facetectomy as the most destabilizing injury, and a stabilizing mechanism of muscle spasm in the beginning and of healing and other adaptive responses in the late phase after injury. Because of the significant differences between the canine model and the human cervical spine, the present findings should be extrapolated to the human situation with caution.

The injured canine cervical spine after six months of healing. An in vitro three-dimensional study.

The cervical spine is a common site of spinal injuries. The stability of an injured cervical spine is not only dependent on injury severity, but also on the degree of healing time. Using a canine model, three injuries of varying degrees of severity were surgically produced at the C4-C5 level and allowed to heal for 6 months. No internal or external support was provided. The harvested cervical spines (C2-C7) were subjected to three-dimensional biomechanical testing by applying individually six pure moments. The resulting three-dimensional displacements were recorded using stereophotogrammetry, and the intervertebral motions were calculated. The results are compared with the in vivo behavior of the same specimens and with an in vitro control group. At 1 N-m, the average flexion-extension range of motion (ROM) for the intact C4-C5 level was 24.5 degrees (standard deviation [SD], 6.6 degrees). A facetectomy at this level significantly increased the in vitro ROM to 51.1 degrees (SD, 4.4 degrees). The in vitro ROM decreased to 19.8 degrees (SD, 7.3 degrees) in the facetectomized group of this study, which were allowed to heal for 6 months before death. Similar results were obtained in axial rotation and lateral bending. The findings show that after 6 months of healing, the injured canine spine, although acutely hypermobile, exhibited biomechanical characteristics that were not different from those of the normal intact specimens.

The effect of radiation on the fracture repair process. A biomechanical evaluation of a closed fracture in a rat model.

The effects of a single dose of irradiation on the biomechanical parameters of the fracture healing process were studied in a rat model. Intramedullary pinning was performed before production of a closed femoral midshaft fracture. The experimental group was exposed to 900 rad 3 days after fracture and was compared with a control group with a similar fracture that received no irradiation. Animals were killed at intervals ranging from 2-16 weeks after surgery and the bones were tested until failure in torsion. In the irradiated groups, a delay of 4 weeks was noted in the biomechanical parameters associated with fracture healing (torque to failure, torsional stiffness, angle to failure, and biomechanical stage). Despite this delay in the normal temporal progression, the staging and stiffness approached normal controls within an 8-week period. However, the torque to failure remained below normal levels at the conclusion of this study. These results differ from a previous study using an open fracture model.

Allograft incorporation: a biomechanical evaluation in a rat model.

Allogeneic bone from Sprague-Dawley rat femurs was subjected to levels of freezing and/or irradiation that are known to have produced changes in the associated immune responses to these grafts. This bone was transplanted into an experimentally created gap in the femur of Lewis rats. The subsequent healing of the transplants in the Lewis rats was studied at 2, 4, 8, and 16 weeks after transplantation using torsion testing to failure. There was no clear advantageous biologic response in the union of the grafted material accompanying the alterations in immunologic response as measured by biomechanical testing of the proximal osteosynthesis site in torsion. The torsional strength of all of these groups remained lower than that of intact bone. Furthermore, none of the frozen and/or irradiated allografts exceeded the strength of the fresh allograft at a statistically significant level.

Biomechanics of the rabbit cervical spine as a function of component transection.

The rabbit cervical spine in the form of the functional spinal unit was tested in a manner analogous to that used to study human functional spinal units. Anatomies and biomechanical similarities and differences with the human were demonstrated. The rabbit cervical spine failed abruptly after a well-defined series of anterior or posterior segmental injuries. However, up to the failure point, the rabbit cervical spine exhibited an increased range of motion after each segmental injury. The results of this study were used to develop an in vivo model for the study of spinal injury in subsequent projects.

Temporal biomechanics of posterior cervical spine injuries in vivo in a rabbit model.

There are numerous clinical and biomechanical criteria for determination of acute spinal instability. No data, however, exist on the biomechanical behavior of the injured, untreated spine during the healing period. Using a rabbit model, this study was designed to quantify changes in the mechanical properties of the injured spine over time. Sixteen rabbits were assigned to four injury groups: Injury 1 (C4-5 supra/intraspinous ligament transection), Injury 2 (C4 laminectomy), or Injury 3 (C4 laminectomy, plus bilateral facet capsular ligament transection). The fourth injury group was Sham (posterior exposure of C4-5, no spinal injury). Preinjury range of motion was determined by standardized flexion-extension radiographs on all animals. Postinjury flexion-extension radiographs were taken at 4, 8, and 12 weeks. At the end of 12 weeks, animals were killed. Mean range of motion at C4-5 for all injury groups decreased from preinjury values. The greatest decrease was for the most severe injury. At 8 weeks, the range of motion for this injury was less than half of the preinjury level and increased to 62% of the preinjury level at 12 weeks.

Biomechanical aspects of bone autografts and allografts.

The structural requirements of skeletal reconstruction should be included in the consideration of an appropriate type of bone graft, whether autogenous or allogeneic tissues are chosen. This analysis should include the nature of any fixation devices to be used, as well as characteristics of the host and donor bone. The mechanical properties and biomechanical response of the graft must be balanced against the type and magnitude of the load to which the graft will be subject. For example, the information presented here suggests that, from a biomechanical perspective, frozen bone would be better suited than freeze-dried bone when the graft is subject to large torsional loads or else the graft must be appropriately protected during incorporation by adequate internal fixation or external bracing. In a situation that is primarily subjected to compressive loads, however, freeze-dried grafts would be just as biomechanically sound. Thus, an understanding of the normal biomechanics of the anatomic region to be reconstructed is crucial. The mechanical properties of the graft are affected by preservation, storage, and sterilization. Incorporation and remodeling of the graft further alter its properties. These properties are, in turn, influenced by the host immune response as well as the local biomechanical environment. The influence of each of these factors is predictable. Obviously, there are numerous considerations in choosing approaches to skeletal reconstruction other than the mechanical issues discussed here. However, an understanding of the mechanical properties involved will help in optimizing the clinical success of these choices.

Indium-111 platelet scintigraphy for the diagnosis of acute venous thrombosis.

Platelets labeled with indium-111 have been used successfully as a marker of active thrombosis in man. To establish the diagnostic accuracy of platelet scintigraphy in comparison to contrast venography in the diagnosis of acute lower limb venous thrombosis, we evaluated 103 consecutive patients divided into two groups. Platelets were labeled by the indium-111 oxine method. Patients from group I (n = 73, 56 had venograms) were asymptomatic and underwent platelet scintigraphy 1.1 +/- 0.6 days (mean +/- 1 SD) after a major orthopedic procedure. Patients from group II (n = 30, all had venograms) were symptomatic and underwent platelet scintigraphy 1.2 +/- 1.7 days after venography. In group II, 15 patients with positive findings on contrast venography were treated with intravenous heparin; five others with positive venograms did not receive heparin until platelet scintigraphy was completed. Both platelet scintigraphy and contrast venography were evaluated by two blinded observers. Only studies with blinded agreement of both platelet scintigraphy and contrast venography were included in the analysis. Sensitivity and specificity of platelet scintigraphy for the whole limb were 93% and 97% in group I and 42% and 67% in group II. The lower sensitivity in group II was most likely attributable to therapy with heparin. These results demonstrate that platelet scintigraphy, a test that permits imaging for up to five days after a single injection, correlates favorably with contrast venography in patients who have not received heparin and may be used as a surveillance test in high-risk patients. The role of platelet scintigraphy in acutely symptomatic patients requires further evaluation.

Three-dimensional load-displacement curves due to forces on the cervical spine.

Load-displacement curves were measured for six types of pure force loading of the cervical spine specimens obtained from fresh human cadavers. A new measuring and mounting technique was developed that yielded data for all of the functional spinal units for each specimen tested. All five of the coupled, as well as the main, load-displacement curves were studied. For anterior and posterior shear loadings, the main resulting motions were translation in that direction (1.6 +/- 0.3 and 1.9 +/- 0.3 mm), and the major coupled motions were flexion and extension (3.6 degrees +/- 1.2 degrees and 6.3 degrees +/- 1.2 degrees). The main motions with right and left lateral shear loadings were translations laterally (1.4 +/- 0.3 and 1.6 +/- 0.3 mm), and the major coupled motions were axial rotations (1.5 degrees +/- 0.6 degrees and 2.3 degrees +/- 0.6 degrees) and not lateral bending. For compression and distraction loadings, the main motions were translations in that direction (0.7 +/- 0.3 and 1.1 +/- 0.3 mm), and the major coupled motions were flexion and extension (2.0 degrees +/- 1.0 degrees and 2.8 degrees +/- 1.0 degrees) and lateral bending (1.4 degrees +/- 0.3 degrees and 1.9 degrees +/- 0.3 degrees). The neutral zones for anterior and posterior shear forces were 1.6 +/- 0.2 mm of translation and 5.8 degrees +/- 1.3 degrees of rotation, for lateral shear force 1.4 +/- 0.3 mm and 2.0 degrees +/- 0.5 degrees, and for compression/distraction 0.6 +/- 0.1 mm and 2.8 degrees +/- 0.9 degrees.