Biological Fixation of a Porous-Coated, Metal-Backed Acetabular Component in Canine Total Hip Arthroplasty

A total hip surface replacement was successfully performed on eight adult dogs, using a porous-coated, cobalt-chromium- molybdenum alloy acetabular resurfacing component fixed to the acetabulum with 3.5 mm cortical screws. Functional, radiological, histological and fluorochrome labelling studies were used to assess tissue response to the implant. At four months after implantation, seven of the acetabular components were anchored with well organized fibrous tissue. Bone ingrowth had occurred in three components. Failures appeared to be due to technical difficulties encountered during the surgical procedure.

Dynamic Strain in the Canine Tibia: an in vivo Strain Gauge Analysis

Electrical resistance rosette strain gauges were bonded directly to the surface of the midshaft of the tibia in four dogs. In vivo strain recording were obtained using a telemetric system allowing the dog relatively free movement. During the stance phase of walking, the cranial surface was mainly in tension while the caudal surface was mainly in compression. The pattern of strain recorded is consistent with craniocaudal bending superimposed on external torsion at the stifle.

Effects of Tapping on the Holding Strength of Cancellous Bone Screws

The purpose of the study was to determine whether tapping affects the holding strength of cancellous bone screws in soft material. Paired extraction tests were conducted using 6.5 mm cancellous bone screws in porous polyurethane foam. One member of each pair had a pre-tapped pilot hole, the other was inserted in a self-tapping manner. The maximum value of tensile force during extraction with a servohydraulic materials testing machine was recorded as the screw holding strength.

Comparison of the holding strengths between the pre-tapped and self-tapping groups revealed a lower mean holding strength for the pre-tapped group (p <0.05). This result contrasts with previous studies which showed that pre-tapping increases the holding strength of bone screws in relatively stronger materials. The effect of tapping on the holding strength of bone screws is therefore dependant on the material properties of the host medium.

This study examined the effect of tapping the pilot hole on the extraction strength of 6.5 mm cancellous bone screws in soft, synthetic cancellous material. In contrast with previous studies in stronger materials, it was found that tapping significantly reduces the holding strength of bone screws. The effects of tapping depend on the material properties of the host medium.

Reliability, validity, and responsiveness of the lower extremity measure for patients with a hip fracture

BACKGROUND

The purpose of this study was to determine whether currently published outcome measures of physical function would be suitable for use for older adults with a hip fracture. The measures that were considered were the Musculoskeletal Function Assessment (MFA) Instrument, the Older Americans' Resources and Services (OARS) Multidimensional Functional Assessment Questionnaire physical function subscale, the Toronto Extremity Salvage Score (TESS), and the Short Form-36 (SF-36). Following suggestions by an expert panel and patient interviews, the MFA was not tested further. The TESS was modified and renamed the Lower Extremity Measure (LEM).

METHODS

Forty-three community-dwelling patients with a hip fracture completed the LEM, OARS, and SF-36 in the hospital so that the prefracture status could be obtained; they were then followed prospectively at six weeks and at six months. All patients were interviewed twice in the hospital to assess the reliability of the LEM (intraclass correlation coefficient = 0.85). To establish criterion validity, the measures were compared with the Timed Up and Go (TUG) test at six weeks. We tested a number of hypotheses to determine construct validity.

RESULTS

Only the LEM scores were significantly correlated with the TUG scores (r = -0.53, p = 0.03). The LEM scores were significantly correlated with the SF-36 subscale scores and the OARS scores. Patients with at least one comorbidity had a lower mean prefracture LEM score (90.0 +/- 9.7) than patients with no comorbidity (96.9 +/- 8.1) (p = 0.02). Patients who had used no walking aids before the fracture had a higher mean prefracture LEM score than those who had used a cane (95.5 +/- 5.8 compared with 85.5 +/- 12.7; p = 0.0007). Both the LEM and the SF-36 scores changed significantly between all of the time-periods (p < 0.05). Measures of responsiveness indicated that the LEM was the best measure for detecting changes in physical function.

CONCLUSIONS

The LEM can detect clinically important changes in physical function over time in patients with a hip fracture and would be most useful for clinical trials or cohort studies. Orthopaedists who are currently utilizing the SF-36 can be reassured that the physical function subscale is a valid measure for patients with a hip fracture.

Acetabular revision. The role of rings and cages

This study reports on the successful long-term use of the acetabular roof ring and the antiprotrusio cage in acetabular reconstruction in which the hip center and acetabular biomechanics are normalized and bone stock is restored through the use of morselized allograft. The failure rate of the acetabular roof ring used in 57 patients who were followed up for a mean of 8.3 years was 12.5%. The failure rate of the antiprotrusio cage used in 38 patients who were followed up for a mean of 6.6 years was 5.4%. The higher failure rate of the acetabular roof ring resulted from its inappropriate use in patients with medial wall deficiency and protrusio. The acetabular roof ring is indicated for patients with isolated peripheral segmental or cavitatory defects. The antiprotrusio cage is indicated for patients with extensive combined segmental and cavitatory defects but particularly for those patients with protrusio and medial segmental bone loss. Both methods have given a high degree of success for evaluation of implant specific, patient subjective, and global health status instruments such as the Short Form-36.

Understanding economic evaluations: a review of the knee arthroplasty literature

The study reviewed the literature to appraise the quality, quantity, and type of economic evaluation as it pertains to the knee arthroplasty literature. A computerized bibliographic search of MEDLINE from 1966-1996 was conducted, revealing a total of 43,178 articles dealing with cost analysis, of which 1611 were orthopedic. Of the economic orthopedic studies, only 63 dealt with the topic of knee arthroplasty. These studies were retrieved, of which only 40 papers met the inclusion criteria. These 40 studies were evaluated for methodological soundness based on established economic principles. None of the 40 studies met the established criteria to form a comprehensive economic evaluation. These results indicate that the orthopedic literature is lacking in economically sound evaluations, and guidelines are offered to aid orthopedists in appraising and improving the quality of economic studies.

Economic evaluations in the hip arthroplasty literature: lessons to be learned

Readers are increasingly encountering articles dealing with health economic evaluations that compare various surgical strategies, leaving orthopaedists with the challenge of determining which program is cost-efficient and truly pertains to their setting. This study carries out a systematic review of the literature to appraise the quality, quantity, and type of economic evaluation as it pertains to the hip arthroplasty literature. To identify all relevant articles, we conducted a comprehensive computerized bibliographic search of Medline from 1966 to 1996. This search produced 1,611 abstracts that were screened. Studies that were incorporated met the following inclusion criteria: i) formal economic analysis, ii) an intervention specific to hip arthroplasty, and iii) the perspective of the study was evident (ie, patient, provider, society). These studies were appraised with regards to methodologic soundness based on 8 established economic principles. Only 68 articles from the 138 retrieved met the study criteria. Only 2 of the 68 articles met all 8 criteria of a comprehensive economic evaluation. The hip arthroplasty literature is deficient in methodologically sound economic evaluations. Several guidelines are introduced to aid orthopaedists in appraising the various economic studies, and recommendations are made to improve the quality of these studies in the orthopaedic literature. We suggest that the generation of such information should rank high on the priority list of the orthopaedic profession, granting agencies, and governments.

Predictors of early failure of fixation in the treatment of displaced subcapital hip fractures

OBJECTIVE

To examine predictors of fixation failure in the treatment of displaced subcapital hip fractures.

DESIGN

Retrospective study.

METHODS

All patients aged sixty-five years and older discharged from a large teaching hospital after treatment for displaced subcapital fracture between April 1, 1989 and February 29, 1995 were identified (n = 344). Of these, 108 patients treated with internal fixation became the study group. Clinical information included demographics, implant, comorbidity, complications, mortality, surgeon' s assessment of reduction, and need for revision. Preoperative x-ray information: Garden grade, Singh Index, Pauwel's angle, medial neck and femoral shaft cortex width, and displacement of fracture fragments. Postoperative: Quality of reduction, a visible gap or step, evidence of union, fracture collapse, and failure.

RESULTS

The failure rate was 31 percent. The two most important predictors were varus reduction and perceived difficulty in achieving reduction. If the patient had a varus reduction or the surgeon had difficulty achieving a satisfactory reduction, fixation was 4.3 times more likely to fail (p = 0.007). If the patient had a varus reduction and reduction was difficult, fixation was 13.6 times more likely to fail (p = 0.04). Under this latter scenario, 75 percent of the fixations failed.

CONCLUSION

In a fracture of the neck of the femur, if difficulty is encountered in obtaining a closed reduction or there is residual varus angulation, the chance of subsequent fixation failure is high. Hemiarthroplasty may be considered in these cases.

Fractures of the distal femur revisited

The treatment of supracondylar fractures is presented, including the most recent developments. The author uses the comprehensive classification of these fractures and explains the method of this classification scheme as a guide to treatment. New surgical approaches and a discussion of the surgical anatomy are presented in detail. The traditional and contemporary methods of reduction and fixation are discussed, and how the need to preserve the blood supply to the soft tissues and bone has led to the development of the modern methods. The biologic and biomechanical reasons for absolutely stable fixation for simple fractures and splinting with bridging plates, the so called bridge plating of multifragmentary fractures are explained as are the technical details of fixation. Discussed in detail are specific variations in treatment methods for the particularly difficult problem of open fractures, fractures above total knee arthroplasty, and fractures in osteoporotic bone.

Temporal trends and geographic variations in surgical treatment of femoral neck fractures

BACKGROUND

The objectives of this study were to examine temporal trends in treatment of femoral neck fractures, factors associated with treatment, and variations in practice patterns among counties and hospitals in Ontario, Canada.

METHODS

Hospital discharge data were analyzed. Cases were defined as age > 50 years with a surgically treated femoral neck fracture between 1981 and 1992 (n = 29,391).

RESULTS

The age-adjusted and sex-adjusted proportion of patients treated with hemiarthroplasty (HA) increased from 45% in 1981 to 61% in 1992 (p < 0.0001). HA is more likely to be performed among women, older patients, and nursing home patients. Among counties there was a 38-fold variation for total hip arthroplasty (0.5-38%) and a 9-fold variation in use of HA (9-83%). The degree of variation in treatment was mainly the result of individual hospitals.

CONCLUSION

The wide regional variations in treatment of femoral neck fractures reflect a lack of consensus in Ontario.

An orthopedic surgeon survey on the treatment of displaced femoral neck fracture: opposing views

OBJECTIVE

To examine the reasons for practice variation in the treatment of displaced femoral neck fractures.

DESIGN

A survey, asking surgeons to choose either hemiarthroplasty or internal fixation for 2 different female patients with a displaced femoral neck fracture.

SETTING

The Canadian Orthopaedic Association Meeting, Halifax, May 1995.

PATIENTS

The scenario in the first patient was of an independent 70-year-old woman with no pre-existing medical conditions. The scenario in the second patient was of a housebound 84-year-old woman with co-morbidity.

MAIN OUTCOME MEASURES

Proportion of surgeons choosing either hemiarthroplasty or internal fixation for each case scenario. Distribution of reasons to explain the treatment decision.

RESULTS

Ninety-nine surgeons responded. For the case of the 70-year-old woman, 47% chose hemiarthroplasty and 53% chose internal fixation (p = 0.60), and for the 84-year-old woman, 96% chose hemiarthroplasty. These findings were consistent within the subgroups of teaching surgeons and community practice surgeons. Surgeons with 10 years or less of practice tended to favour hemiarthroplasty whereas those with more than 15 years' practice favoured internal fixation. Important reasons for treatment choice were avoidance of reoperation in the hemiarthroplasty group (85%) and better hip function in the fixation group (83%), durability (83%) and ease of revision (77%).

CONCLUSION

The surgeon's interpretation of the importance of reoperation and function underlies the differences in treatment decision regarding the management of femoral neck fractures in elderly patients.

Appropriateness of primary total hip and knee replacements in regions of Ontario with high and low utilization rates

OBJECTIVE

To compare the appropriateness of case selection for primary hip and knee replacements between two regions in Ontario: one with a high population-based utilization rate and one with a low rate.

DESIGN

Random audit of medical records sampled from hospital discharge abstracts, with subsequent implicit and explicit criteria-based assessments of the appropriateness of surgery.

STUDY POPULATION

People aged 60 years or over who underwent elective, single-joint, non-fracture-related, primary hip or knee replacement between Apr. 1, 1992, and Mar. 31, 1993, at one of seven hospitals in a high-rate region (comprising Brant, Huron and Oxford countries) or one of eight hospitals in a low-rate region (comprising the cities of Scarborough and Toronto).

INTERVENTIONS

Structured review of hospital medical records, with additional review of information from surgeons and family physicians' office charts if necessary. Three physicians reviewed patient data and rated the preoperative pain level and functional status of patients, with agreement among at least two reviewers. The proportion of inappropriate cases was then assessed according to explicit criteria defined by a multidisciplinary panel using the delphi process. Profiles of each case were also subjected to independent implicit review by two rheumatologists and two orthopedic surgeons.

OUTCOME MEASURES

Proportion of joint replacements deemed inappropriate in the high- and low-rate regions according to either the explicit criteria or the implicit review, as well as preoperative pain levels and functional status of patients in the high- and low-rate regions.

RESULTS

Hip replacements were more common among patients sampled in the low-rate region than among those in the high-rate region (57.3% v. 39.3%; p < 0.002), although the patients' baseline characteristics, including severity of preoperative pain and dysfunction, were otherwise similar between the regions. Inappropriate surgery, determined by explicit criteria, was equally uncommon in the two regions (6.4% and 6.1%). On implicit review, the two rheumatologists rated fewer cases as appropriate than did the two orthopedic surgeons (63.0% v. 80.0%; p < 0.001); however, the proportion of cases rated as inappropriate by the subspecialists was similar in the high- and low-rate regions (11.4% and 11.0%, respectively, by the rheumatologists, and 6.3% and 10.4%, respectively, by the orthopedic surgeons).

CONCLUSIONS

Patients selected for primary hip or knee replacement are similar in the high- and low-rate regions of Ontario. Inappropriate use of this procedure does not account for the high rate of surgery in some areas. Further studies will be required to determine which other factors account for the regional variations in the utilization rates and whether there is underservicing in low-rate areas.

The impact and consequences of hip fracture in Ontario

OBJECTIVES

To assess the magnitude and the burden of hip fracture on the health care system, including time trends in hip fracture rates, in-hospital death rates, length of hospital stay (LHS) and discharge destination.

DESIGN

A retrospective study of discharge abstracts.

SETTING

The Province of Ontario.

PATIENTS

All patients (n = 93,660) over the age of 50 years and with a diagnosis of hip fracture discharged from hospital between 1981 and 1992 (excluding transfers).

MAIN OUTCOME MEASURES

Age-sex standardized hip fracture rates per 1000 population, in-hospital death rates and age-adjusted mean LHS.

RESULTS

The overall hip fracture rate was 3.3 per 1000 persons (1.7 per 1000 men and 4.6 per 1000 women). There was no change in rates between 1981 and 1992 (p = 0.089), but there have been increases in the numbers of hip fractures. There was no change in the in-hospital death rate over time (p = 0.78). The age-adjusted mean LHS in 1981 was 28.6 days compared with 22.2 days in 1992. The numbers of hip fractures will increase from 8490 in 1990 to 16 963 in 2010.

CONCLUSIONS

Despite stable age-adjusted rates of hip fractures, the doubling of the number of hip fractures by the year 2010 due to an aging population will become an increasing burden on the health care system.

The strength of plate fixation in relation to the number and spacing of bone screws

Our purpose was to study the relationship between the number of plate holes filled and the spacing between the screws and the resultant strength of plated constructs. Broad regular DC plates were anchored with 4.5-mm cortical screws to blocks of polyurethane foam. Six constructs were tested: (a) screws in holes 1, 2, and 3; (b) screws in holes 1 and 3; (c) screws in holes 1 and 4; (d) screws in holes 1 and 5; (e) screws in holes 1 and 6; (f) screws in holes 1, 3, and 5. The strength was quantified using a material-testing system. In cantilever and four-point bending, the constructs were loaded in both gap-closing and gap-opening modes. Screws in holes 1, 2, and 3 were tested against other constructs. For cantilever bending (gap opening and gap closing), construct (a) was stronger than construct (b), as strong as construct (c), but weaker than the constructs with more widely spaced screws (p < 0.0001). In terms of four-point bending, for gap opening, the standard fixation (construct (a) was stronger than construct (b) but weaker than the more widely spaced constructs. For gap closing, construct (a) was stronger than constructs (b) and (c) but weaker than the rest. Regardless of the spacing of screws and the plate length, strength in torsion was dependent on the number of screws securing the plate. In a laboratory fracture model of plate-bone constructs tested to failure by screw pullout, wider spacing of bone screws increases the bending strength of screw-plate fixation and can be more effective than increasing the number of screws. Torsional strength is independent of screw placement in plates of a given width and depends on the number of screws used.

Sample size estimates for the use of human bone in the experimental study of cancellous screw extraction mechanics

Cancellous bone screw extraction strengths are determined in four matched anatomical locations in five pairs of unembalmed human distal femora. The results are used to calculate sample size estimates for the experimental detection of differences in screw extraction mechanics. While unmatched designs require prohibitively large numbers of bone specimens, matched designs require between 71.6 and 88.5% fewer, depending on the correlation between matched observations and the homogeneity of sample variances.

Radiographic appearance and structural properties of proximal femoral bone in total hip arthroplasty patients

The relationship between the morphology of the proximal femur and the physical properties of intertrochanteric trabecular bone was assessed in 26 patients undergoing total hip arthroplasty. Significant correlations were found between ash density and (1) Singh index, (2) "calcar-to-canal isthmus ratio," and (3) a modified "morphologic cortical index." Despite this, these radiographic indices accounted for only 30% of the variability in bone density and are therefore of limited predictive value in this context. Two indices of cortical morphology were at least as effective as the Singh index in predicting cancellous bone density. Surgeons using these indices to quantify the morphology and structure of proximal femoral bone should be aware of their limitations when selecting patients for cementless arthroplasty.

Ceramic head failure

A case of abrupt failure of the ceramic head component of a total hip arthroplasty is reported. The prosthesis had been inserted more than 5 years previously and had functioned well until its abrupt failure. At revision, the metal femoral and acetabular components were intact and well fixed. The broken ceramic head was replaced with a metal component, and the polyethylene liner replaced with a new one.

Osseointegration of metal

The healing response of bone to the injury of implant insertion is similar to its response to fracture. If there is absolute stability between the bone and the implant, the injury to the bone will result in bone formation, the bone growing and conforming to the surface configuration of the implant. There is first appositional bone growth and subsequently bone ingrowth into the interstices of the surface. The newly formed bone is not an uninterrupted layer of bone. It is mixed with well-differentiated fibrous tissue; only 13% to 20% of the bone is in contact with the implant. If the implant is relatively stable after insertion the healing response results in the implant becoming enveloped by dense organized fibrous tissue with occasional areas of fibrocartilage, without any areas of resorption in the surrounding bone. If the implant is unstable after insertion the healing response causes the implant to become surrounded by loosely organized fibrous tissue with active bone resorption occurring in the surrounding bone.

Rapidly destructive arthropathy followed by heterotopic ossification. A case report and literature review

This is the first reported case of heterotopic ossification following total hip replacement for bilateral, rapidly destructive arthropathy of the hip. The aetiological theories of this rare condition are discussed, particularly with reference to this complication.

A case of fracture of a ceramic head in total hip arthroplasty

We report a case of fracture of a ceramic femoral head, which spontaneously occurred 4 years after implantation of an uncemented total hip replacement in a 48-year-old male patient with avascular necrosis of the hip. At revision surgery, the fractured ceramic head was replaced with a 32-mm metallic femoral head.

Acetabular fractures in the elderly: an easily missed diagnosis

Two case reports of low-energy acetabular fractures in elderly people are presented. Both fractures were initially missed because standard hip radiographs were interpreted to be normal. Furthermore, the clinical findings were not strong enough to give the impression of a hip joint fracture. If there is pain in the hip region after a fall, in combination with the absence of clinical findings, appropriate radiographs should be taken to look for acetabular trauma.

Biomechanical analysis of a distally interlocked press-fit femoral total hip prosthesis

This study was undertaken to compare the stability of a distally interlocked femoral prosthesis to a standard press-fit implant (Cementless Spotorno, Protek Co., Toronto, Canada). Five human femora were studied with each acting as its own control. All were tested in the locked mode followed by unlocked testing modes. The MTS 858 Biomaterials Testing System was used to test the implanted femoral stems under both pure torsional and pure axial loading. Distal interlocking increased the torsional stability by 320% (locked 4.05 Nm/degree; unlocked 1.25 Nm/degree) (P < .01) and the axial stability by 230% (locked 1,236.26 N/mm; unlocked 527.44 N/mm) (P < .01). the use of temporary distal interlock in cases where the initial stability of a press-fit implant is suboptimal should allow for improved biological fixation by minimizing micromotion at the stem-bone interface.

Extraction strength of cannulated cancellous bone screws

The purpose of this study was to determine whether the alterations in the relative dimensions of thread and core diameter that accompany cannulation of cancellous bone screws affect their holding strength. The screws were inserted in bovine femoral cancellous bone and mounted in the load train of a materials testing system. They were then extracted under servo-hydraulic displacement control. The tests were repeated in synthetic cancellous material. From the corresponding load-displacement histories, the maximum force values attained were determined as the screws' holding strengths. The results of tests from 17 matched pairs of bovine femora, and of 15 tests of each screw in synthetic material, were recorded. No significant differences in extraction strength between 7.0-mm cannulated and 6.5-mm standard cancellous bone screws were found. Based on tests in the bovine femur and synthetic cancellous material, this study showed that the extraction strength of cancellous bone screws is not altered by the changes in thread-to-core ratio accommodating cannulation.

Subcapital fracture of the hip after internal fixation of an intertrochanteric fracture. A case report

We report a case of a subcapital fracture that occurred after reduction and fixation of an intertrochanteric fracture of the hip with a sliding screw. The subcapital fracture occurred 4 months after surgery for the intertrochanteric hip fracture. The subcapital fracture was undisplaced and occurred in an area supported by the screw without damaging the implant. This patient was treated conservatively with bedrest.

The use of reinforcement rings to reconstruct deficient acetabula

We reviewed 64 patients in whom 66 acetabula had been reconstructed with either the Müller ring (46) or the Burch-Schneider anti-protrusio cage (20) at a mean follow-up of five years. Five hips had been revised a second time for loosening, all after a Müller ring had been used for a medial segmental defect (2), ungrafted cavitary defects (2) or after resorption of a block graft (1). The use of bone grafts with the implants reduced the incidence of failure from 13% to 6% and of circumferential radiolucent lines at the bone-implant interface from 39% to 2%. The Müller ring is indicated for acetabula with isolated peripheral segmental defects or cavitary defects confined to one or two sectors. The Burch-Schneider cage should be used for medial segmental defects, extensive cavitary defects and combined deficiencies. Defects should be reconstituted with bone graft rather than cement.

[Analysis of the "user friendliness" of the AO classification of fractures]

The AO-classification of long bone fractures has been introduced as a universal system and depends mainly on morphological characteristics and fracture-location. It includes the fracture severity and outcome and should be a basis for treatment. To evaluate the AO-classification in the "daily use", we were interested if this system is really userfriendly, where the problems of coding occur and which is the agreement in different codings of several surgeons in relation to segment, type, group and subgroup. 58 fractures were classified, totally we got 456 classifications. The agreement in relation to segment was 95%, to type 79%, to group 63% and to the subgroup only 45%. Endsegment-fractures had a better agreement than shaft fractures. Common mistakes are discussed and some "user-guidelines" are given.

Nonunion of a complex tibial plateau fracture

Nonunion of tibial plateau fractures are uncommon; only five cases have been reported in the literature. This report presents the sixth nonunion and highlights the management of an angulated, periarticular pseudoarthrosis. Pitfalls in the initial fracture treatment that contributed to the development of the pseudoarthrosis are reviewed.

Intraarticular malunions and nonunions

The principles of intraarticular fracture care and stable internal fixation, when applied to intra-articular nonunions and malunions, can result in the restoration of an amazing function to joints that seem almost totally doomed to either an arthrodesis or an arthroplasty. The high degree of success achieved in almost all cases illustrates the amazing recuperative powers of human joints once articular cartilage congruence and stability is re-established together with correction of axial deformities and the mobilization of joints.

The effects of motion on the healing of cancellous bone

In 20 dogs olecranon osteotomies fixed with tension band wires were studied histologically to reveal the pattern of healing. Different degrees of stability existed in different areas of the osteotomy. Under stable conditions cancellous bone healed by direct formation of woven bone. Instability resulted in an internal cartilaginous callus. Once stability was restored, the callus underwent endochondral ossification. The articular defect, which was in an area of maximum instability, healed by fibrocartilage.

Dynamic condylar screw: a new device. A preliminary report

The dynamic condylar screw (DCS) is a new implant engineered by the AO/ASIF Group for use in management of proximal and distal femoral fractures. This device has some technical advantages over the AO condylar blade plate. In a prospective study we reviewed the use of the DCS in the treatment of supracondylar fractures, intertrochanteric fractures, subtrochanteric fractures, nonunions, and malunions in 18 patients (19 femora). The results are based on an average follow-up of 9 months. Seventeen femurs went on to clinical and radiological union with good functional results. There were two failures because of delayed unions.

Supracondylar fracture of the femur after GUEPAR total knee arthroplasty. A new treatment method

A 71-year-old woman incurred an unstable, comminuted supracondylar fracture of the femur above the tip of a GUEPAR prosthesis. The prosthesis was not loose. Immediate open reduction and internal fixation were performed using a segment cut from an intramedullary rod. This provided axial alignment and functioned as an internal stent with stable fixation of the fracture. Supplementary fixation with a plate and screws, cerclage wires, and an autogenous bone graft led to early mobilization, solid bony union, and an excellent functional result.

An experimental investigation in the dog into the mode of osseous integration of total joint implants

An uncemented scaled down version of the Mueller SLS femoral component was inserted into 30 dogs. The material (Protasul 100), geometry, and finish were identical to those designed for clinical use. Half of the prostheses inserted were fitted out with a modular collar to improve stability. Initial stability was achieved through press fit which was made possible by the special modification of the surface area and external configuration of the prosthesis. The function of the prosthesis was assessed through clinical assessment and force plate gait analysis. This was correlated with the degree of osseous integration which was evaluated on the basis of regular radiological examinations, and at post mortem by microradiography of the serially sectioned undecalcified femurs, and histological examination of selected sections under regular and ultraviolet light. The animals were sacrificed at 4, 8, and 12 months. Force plate gait analysis revealed that all animals walked with a normal gait by the 4th post-operative month. Evaluation revealed that 29/30 femoral prostheses became successfully integrated. The prostheses without the collar were less stable and most achieved stability only by incorporation of the distal tip of the prostheses in bone and the remainder in dense fibrous tissue. The prostheses with the collar were stable and achieved without fail full bony integration. The stability was provided by appositional growth of bone which came into direct contact with the implant over the proximal 1/3 and the distal 1/3 without an intervening fibrous membrane. Despite failure of full integration of the collarless prostheses clinically and by force plate analyses the two groups were indistinguishable.(ABSTRACT TRUNCATED AT 250 WORDS)

A strain-gauge study of the effect of external fixation on the canine tibia

Electrical resistance rosette strain gauges bonded directly to the surface of the midshaft of the normal canine tibia were utilized to study the effect of the AO external skeletal fixator on the magnitude and orientation of the peak strain values recorded during locomotion. The application of the fixator in a single lateral bar configuration resulted in a significant decrease in surface bone strain magnitude but in only minor changes in the orientation of those strains. However, in only one of three dogs tested did the addition of a second external connecting bar result in significant further decreases in bone strain.

Apparent changes in the alignment of the femoral component in hip arthroplasties associated with limb positioning

Three femoral components (one cemented and one uncemented straight-stem Muller and one uncemented Anatomic Medullary Locking) were placed into cadaveric or commercially available plastic femora to establish that rotation of the femur can simulate changes in femoral component alignment on the anteroposterior radiograph. The change in alignment is governed by the position of the prosthesis within the femoral canal. If the stem of the prosthesis is positioned posteriorly in the canal, external rotation simulates valgus; internal rotation results in a varus orientation. If the prosthetic stem is located anteriorly in the canal, the reverse is true. This effect was noted in all specimens for values as small as 20 degrees of rotation. Because a change in the position of a prosthesis may signify loosening, it is recommended that standardized positioning techniques be used for radiographic analysis of total hip arthroplasties.

Intermediate results of a straight stem prosthesis in primary total hip arthroplasty

In a retrospective study of 130 primary total hip arthroplasties with a self-locking straight stem femoral component (Muller) and low profile cup, the average follow-up evaluation was 3.1 years (range, 2.0-4.6 years). According to the clinical rating system modified from Swanson and Evarts, there were 115 (88.3%) excellent, six (4.7%) good, four (3.1%) fair, and five (3.9%) poor results. Radiolucent lines at least 1 mm in width were noted in 12.8% of acetabula, mostly in Zones 1 and III. One cup has been revised and one is awaiting revision. Radiolucent lines greater than or equal to 1 mm were noted around 26.5% of femoral components. These were asymptomatic, unless associated with the presence of infection, subsidence greater than 5 mm, or symptoms of acetabular loosening. True femoral subsidence was pain free and nonprogressive in seven patients (6%) if less than or equal to 5 mm. Femoral loosening was roentgenographically observed as component migration or subsidence greater than 5 mm. By these criteria, three femoral components (2.6%) were loose, although none have been revised.

Wagner resurfacing arthroplasty of the canine hip

Twelve surface replacement arthroplasties were performed on the hips of ten mongrel dogs using scaled-down replicas of the Wagner prosthesis. The contralateral hips and two further animals served as nonoperated controls. Animals were killed 5 months postoperatively. Clinical, radiological, histological and fluorochrome-labelling studies were employed to assess the bony and soft tissue reaction to resurfacing arthroplasty. There was no clinical or radiographic evidence of prosthetic loosening. Histological examination disclosed a thick foreign body and chronic inflammatory membrane containing acrylic cement and polyethylene wear particles at the bone-cement interface of both components. Generally, the bone marrow and trabecula were viable. There was evidence of increased bony remodelling and new bone formation in the subchondral area. The similarity between the above findings and those of aseptic component loosening in man suggests a mechanism whereby wear debris initiate a biological foreign body reaction culminating in component loosening.

Revision hip surgery using the straight-stem Muller prosthesis

Thirty-two cemented revision hip arthroplasties done with a straight-stem Muller prosthesis were reviewed an average of 3 years after operation (range, 2-4.4 years). Acetabular revision, performed in 29 cases, we done with a support ring, mesh, or bone graft in 18 of 29 (62%) cases. Acetabular and femoral cement pressurization techniques were not used. Trochanteric osteotomy was done in 15 cases (47%). The average patient age was 60.2 years (range, 20-85 years). Based on the clinical rating system of Swanson and Evarts, there were 21 (65.6%) excellent, 2 (6.3%) good, 8 (25%) fair, and 1 (3.1%) poor results. The clinical outcome was better after revision from a resurfacing arthroplasty (87.5% good/excellent results) than from uni/bipolar or total hip arthroplasty (60%). Radiographic examination suggests that two femoral components and one acetabular component are loose. These patients have a fair clinical rating. None have been revised. Trochanteric wire breakage (60%) and displacement (26.7%) was common if trochanteric osteotomy was done.

Internal fixation of femoral neck fractures: a prospective study

To determine the adequacy of reduction and the soundness of the technique of primary internal fixation, the authors studied prospectively 96 femoral neck fractures over 6 1/2 years. Patients were followed up for an average of 11 months. The mean patient age was 70 years. Both clinical and radiologic data were collected at 3-month intervals for 6 months and then annually. Radiologic indices recorded included the Garden classification and index, shear angle, Western Infirmary Glasgow angle, lateral angle, nail placement, occurrence of bony union and presence of avascular necrosis. The fixation devices included sliding compression screw and side plate, multiple Knowles pins and a 130 degrees AO blade plate. A high rate of varus reduction, excessive ante- or retroversion and poor nail placement were all noted. Twenty-three patients required a total of 36 reoperations. There were six deaths in the first 6 months after operation. Eighty-five patients (mean age 79 years) with femoral neck fractures treated by hemiarthroplasty (71) or total hip replacement (14) during the same period were also reviewed. Follow-up averaged 8 months. Two patients required reoperation. The general morbidity was similar to that of the group treated by internal fixation, but there were eight deaths. Femoral neck fractures, if treated by internal fixation, demand accurate reduction and fixation for optimum results. Primary prosthetic replacement should be reserved for elderly patients with poor bone stock.

Fracture of a polyethylene acetabular cup: a case report

Fracture of a polyethylene acetabular cup is rare. Current theories of its cause emphasize wear of the component. The case reported illustrates the presence of a loosening membrane in association with cup fracture. Histologic study of the loosening membrane indicated a foreign-body reaction to polyethylene and acrylic wear particles. The authors propose a theory relating micromotion of the acetabular component to the production of particles of wear with a subsequent foreign-body reaction followed by further loosening. The erosion of bony support leads to the concentration of stress at the junction of the supported and unsupported segments. This may ultimately result in fracture of the cup.

A study of implant failure in the Wagner resurfacing arthroplasty

Using clinical, radiographic, and pathological data, we investigated eighteen cases of early aseptic failure of an implant in patients who had undergone reconstruction of the hip with a Wagner resurfacing prosthesis. Sixteen patients required revision for loosening of the acetabular component, with eight of them also demonstrating loosening of the femoral component. One patient had loosening of the femoral component without failure of the acetabular component, and one patient sustained a femoral neck fracture that was associated with osteonecrosis. Six of the patients with loosening of the acetabular component had an associated significant loss of acetabular bone stock. Loosening was associated with the development of a membrane at the bone-cement interface in all patients. Histological examination of the membrane demonstrated a marked foreign-body response to wear products from the arthroplasty. Bone resorption appeared active at the bone-membrane interface. We concluded that the acetabular component of the Wagner prosthesis is prone to early loosening and that the early loosening is potentiated by a foreign-body response to debris resulting from arthroplastic wear.

The effect of polymethylmethacrylate on bone: an experimental study

In order to assess the response of bone to low-viscosity polymethylmethacrylate, CMW or Simplex acrylic cement was digitally packed while in a doughy state into drill holes in the proximal diaphysis in each of four long bones (humeri and tibiae) of mongrel dogs. Histological assessment was performed in areas of minimal load at the interface between the viscoelastic bone and the acrylic cement. Decalcified and undecalcified sections were evaluated and a remodeling or activity index calculated. Fluorescent labeling studies were performed in order to assess bone growth. Animals were killed at 2, 4 or 5 months. Histological analysis showed a thin connective-tissue membrane containing scattered giant cells and histiocytes at the bone-cement interface. Inflammation was not an important facet of this response. The marrow and trabecular bone were viable, except for scattered localized areas of marrow necrosis and fibrosis immediately adjacent to the cement. The bone adjacent to the cement showed a lower remodeling or activity index, fewer fluorescent bands, and smaller distances between successive bands, suggesting decreased bone formation and turnover. The etiology of these findings may include a vascular disturbance secondary to disruption of the cortical and marrow circulation, temperature effects during cement polymerization, and/or chemical effects from the acrylic monomer.

Popliteal artery entrapment

Images

The management of nonunions following high tibial osteotomies

Nonunion is an uncommon complication of high tibial osteotomy. Reported techniques of treating such a complication include resection of the pseudarthrosis and cast immobilization with risk of joint stiffness and loss of alignment. The special AO/ASIF threaded external fixator with double clamps was used to treat three patients with nonunions following high tibial osteotomy for medial compartment osteoarthritis. The pseudarthrosis was not resected in any instance. All were allowed full unrestricted joint motion postoperation. Rapid healing of the osteotomy ensued. The external fixator achieved excellent stability and rapid union while maintaining joint motion.

A preliminary review of the Müller acetabular and Burch-Schneider antiprotrusio support rings

A high incidence of acetabular loosening following total hip arthroplasty is emerging as long term follow-up studies become available. The Müller and Burch-Schneider acetabular supports are indicated for acetabular deficiencies which are frequently present during revision hip arthroplasty. The Burch-Schneider support is indicated where the deficiencies are of such magnitude that the Müller ring does not have stable seating prior to screw fixation. These devices bring the resultant of forces across the hip joint under the acetabular roof and provide metal backing for the acetabular cup. They have the additional advantage of screw fixation which in the Müller ring is in line with the resultant of forces across the hip joint. In a one to three year follow-up of twenty-five hip replacements in twenty-four patients, the Müller support ring was used in twenty hips and the Burch-Schneider in five hips. The results were satisfactory and indicate that these supports are valuable in the treatment of patients with acetabular deficiencies.

A randomized trial of manipulation for low-back pain in a medical setting

The authors carried out a single-blind, randomized controlled clinical trial of rotational manipulation for low-back pain of recent onset in 81 adults. Control treatments were minimal massage and low-level electrostimulation. Initial status and outcome were measured on scales quantifying symptoms, activities of daily life, mobility, tenderness to palpation, aggravation of pain by coughing or sneezing, limitation of motion on testing, and forward flexion. Both treated and control patients improved rapidly in the 2-3-week observation period. On retest there was no statistically significant difference between the improvement scores of the treated or control groups on any of the scales.

Revision of total hip arthroplasty

Between September 1978 and December 1980, 28 revision procedures were carried out at the Wellesley Hospital, Toronto, for biomechanical failure of total hip arthroplasties. Twenty-six patients were personally reviewed and assigned a Harris hip rating. Seven patients had major complications intraoperatively or postoperatively; three of them required further surgery. Twenty-four patients had satisfactory results and none were worse. The mean Harris score preoperatively was 36.3. At a minimum follow-up of 1 year after revision, the mean Harris score rose to 79.9 (p less than 0.01). Revision of total hip arthroplasty is a difficult and demanding procedure but can produce satisfactory results.