'Bundle busters': who is at risk of exceeding the target payment and can they be optimized?

AIMS: The Bundled Payments for Care Improvement (BPCI) initiative has identified pathways for improving the value of care. However, patient-specific modifiable and non-modifiable risk factors may increase costs beyond the target payment. We sought to identify risk factors for exceeding our institution's target payment, the so-called 'bundle busters'. PATIENTS AND METHODS: Using our data warehouse and Centers for Medicare and Medicaid Services (CMS) data we identified all 412 patients who underwent total joint arthroplasty and qualified for our institution's BPCI model, between July 2015 and May 2017. Episodes where CMS payments exceeded the target payment were considered 'busters' (n = 123). Risk ratios (RRs) were calculated using a modified Poisson regression analysis. RESULTS: An increased risk of exceeding the target payment was significantly associated with increasing age (adjusted RR 1.04, 95% confidence interval (CI) 1.01 to 1.06) and body mass index (adjusted RR 1.03, 95% CI 1.003 to 1.06). Eight comorbid risk factors were also identified (all p < 0.05), only two of which were considered to be potentially modifiable (diabetes with complications and preoperative anaemia). An American Society of Anesthesiologist physical status classification system (ASA) score ≥ 3 (adjusted RR 2.3, 95% CI 1.67 to 3.18) and Charlson Comorbidity Index (CCI) ≥ 3 (adjusted RR 1.94, 95% CI 1.45 to 2.60) were risk factors for bundle busting. CONCLUSION: Non-modifiable preoperative risk factors can increase costs and exceed the target payment. Future bundled payment models should incorporate the stratification of risk. Cite this article: Bone Joint J 2019;101-B(7 Supple C):64-69.

Correction of mildly dysplastic hips with periacetabular osteotomy demonstrates promising outcomes, achievement of correction goals, and excellent five-year survivorship.

AIMS: The aim of this study was to compare patient-reported outcome measures (PROMs), radiological measurements, and total hip arthroplasty (THA)-free survival in patients who underwent periacetabular osteotomy (PAO) for mild, moderate, or severe developmental dysplasia of the hip. PATIENTS AND METHODS: We performed a retrospective study involving 336 patients (420 hips) who underwent PAO by a single surgeon at an academic centre. After exclusions, 124 patients (149 hips) were included. The preoperative lateral centre-edge angle (LCEA) was used to classify the severity of dysplasia: 18° to 25° was considered mild (n = 20), 10° to 17° moderate (n = 66), and < 10° severe (n = 63). There was no difference in patient characteristics between the groups (all, p > 0.05). Pre- and postoperative radiological measurements were made. The National Institute of Health's Patient Reported Outcomes Measurement Information System (PROMIS) outcome measures (physical function computerized adaptive test (PF CAT), Global Physical and Mental Health Scores) were collected. Failure was defined as conversion to THA or PF CAT scores < 40, and was assessed with Kaplan-Meier analysis. The mean follow-up was five years (2 to 10) ending in either failure or the latest contact with the patient. RESULTS: There was no significant difference in PROMs for moderate (p = 0.167) or severe (p = 0.708) groups compared with the mild dysplasia group. The numerical pain scores were between 2 and 3 units in all groups at the final follow-up (all, p > 0.05). There was no significant difference (all, p > 0.05) in the proportion of patients achieving target correction for the LCEA between groups. The mean correction was 12° in the mild, 15° in the moderate (p = 0.135), and 23° in the severe group (p < 0.001). Failure-free survival at five years was 100% for mild, 79% for moderate, and 92% for severely dysplastic hips (p = 0.225). CONCLUSION: Although requiring less correction than hips with moderate or severe dysplasia, we found PAO for mild dysplasia to be associated with promising PROMs, consistent with that of the general United States population, and excellent survivorship at five years. Future studies should compare these results with the outcome after arthroscopy of the hip in patients with mild dysplasia. Cite this article: Bone Joint J 2019;101-B(6 Supple B):16-22.

Ten-year survivorship of primary total hip arthroplasty in patients 30 years of age or younger.

Aims: For this retrospective cohort study, patients aged ≤ 30 years (very young) who underwent total hip arthroplasty (THA) were compared with patients aged ≥ 60 years (elderly) to evaluate the rate of revision arthroplasty, implant survival, the indications for revision, the complications, and the patient-reported outcomes. Patients and Methods: We retrospectively reviewed all patients who underwent primary THA between January 2000 and May 2015 from our institutional database. A total of 145 very young and 1359 elderly patients were reviewed. The mean follow-up was 5.3 years (1 to 18). Logistic generalized estimating equations were used to compare characteristics and the revision rate. Survival was evaluated using Kaplan-Meier curves and hazard rates were created using Cox regression. Results: The overall revision rate was 11% (16/145) in the very young and 3.83% (52/1359) in the elderly groups (odds ratio (OR) 2.58, 95% confidence interval (CI) 1.43 to 4.63). After adjusting for the American Society of Anesthesiologists (ASA) score, gender, and a history of previous surgery in a time-to-event model, the risk of revision remained greater in the very young (adjusted hazard ratio (HR) 2.48, 95% CI 1.34 to 4.58). Survival at ten years was 82% (95% CI, 71 to 89) in the very young and 96% (95% CI, 94 to 97) in the elderly group (p < 0.001). The very young had a higher rate of revision for complications related to metal-on-metal (MoM) bearing surfaces (p < 0.001). At last follow-up, the very young group had higher levels of physical function (p = 0.002), lower levels of mental health (p = 0.001), and similar levels of pain (p = 0.670) compared with their elderly counterparts. Conclusion: The overall revision rate was greater in very young THA patients. This was largely explained by the use of MoM bearings. Young patients with non-MoM bearings had high survivorship with similar complication profiles to patients aged ≥ 60 years. Cite this article: Bone Joint J 2018;100-B:867-74.

Patient-specific chondrolabral contact mechanics in patients with acetabular dysplasia following treatment with peri-acetabular osteotomy.

OBJECTIVE: Using a validated, patient-specific finite element (FE) modeling protocol, we evaluated cartilage and labrum (i.e., chondrolabral) mechanics before and after peri-acetabular osteotomy (PAO) to provide insight into the ability of this procedure to improve mechanics in dysplastic hips. DESIGN: Five patients with acetabular dysplasia were recruited in this case-controlled, prospective study. Models, which included anatomy for bone, cartilage, and labrum, were generated from computed tomography (CT) arthrography scans acquired before and after PAO. Cartilage and labrum contact stress and contact area were quantified overall and regionally. Load supported by the labrum, expressed as a percentage of the total hip force, was analyzed. RESULTS: Percent cartilage contact area increased post-operatively overall, medially, and superiorly. Peak acetabular contact stress decreased overall, laterally, anteriorly, and superiorly. Average contact stress decreased overall, laterally, anteriorly, and posteriorly. Only average contact stress on the superior labrum and peak labrum stress overall decreased. Load supported by the labrum did not change significantly. CONCLUSIONS: PAO was efficacious at medializing cartilage contact and reducing cartilage contact stresses, and therefore may minimize deleterious loading to focal cartilage lesions, subchondral cysts, and cartilage delaminations often observed in the lateral acetabulum of dysplastic hips. However, the excessively prominent, hypertrophied labrum of dysplastic hips remains in contact with the femoral head, which continues to load the labrum following PAO. The clinical ramifications of continued labral loading following PAO are not known. However, it is plausible that failure to reduce the load experienced by the labrum could result in end-stage hip OA following PAO.

Computed tomography arthrography with traction in the human hip for three-dimensional reconstruction of cartilage and the acetabular labrum.

AIM: To develop and demonstrate the efficacy of a computed tomography arthrography (CTA) protocol for the hip that enables accurate three-dimensional reconstructions of cartilage and excellent visualization of the acetabular labrum. MATERIALS AND METHODS: Ninety-three subjects were imaged (104 scans); 68 subjects with abnormal anatomy, 11 patients after periacetabular osteotomy surgery, and 25 subjects with normal anatomy. Fifteen to 25 ml of contrast agent diluted with lidocaine was injected using a lateral oblique approach. A Hare traction splint applied traction during CT. The association between traction force and intra-articular joint space was assessed qualitatively under fluoroscopy. Cartilage geometry was reconstructed from the CTA images for 30 subjects; the maximum joint space under traction was measured. RESULTS: Using the Hare traction splint, the intra-articular space and boundaries of cartilage could be clearly delineated throughout the joint; the acetabular labrum was also visible. Dysplastic hips required less traction (∼5 kg) than normal and retroverted hips required (>10 kg) to separate the cartilage. An increase in traction force produced a corresponding widening of the intra-articular joint space. Under traction, the maximum width of the intra-articular joint space during CT ranged from 0.98-6.7 mm (2.46 ± 1.16 mm). CONCLUSIONS: When applied to subjects with normal and abnormal hip anatomy, the CTA protocol presented yields clear delineation of the cartilage and the acetabular labrum. Use of a Hare traction splint provides a simple, cost-effective method to widen the intra-articular joint space during CT, and provides flexibility to vary the traction as required.

Patient-specific analysis of cartilage and labrum mechanics in human hips with acetabular dysplasia.

BACKGROUND: Acetabular dysplasia is a major predisposing factor for development of hip osteoarthritis (OA), and may result from alterations to chondrolabral loading. Subject-specific finite element (FE) modeling can be used to evaluate chondrolabral mechanics in the dysplastic hip, thereby providing insight into mechanics that precede OA. OBJECTIVE: To evaluate chondrolabral contact mechanics and congruency in dysplastic hips and normal hips using a validated approach to subject-specific FE modeling. METHODS: FE models of ten subjects with normal acetabula and ten subjects with dysplasia were constructed using a previously validated protocol. Labrum load support, and labrum and acetabular cartilage contact stress and contact area were compared between groups. Local congruency was determined at the articular surface for two simulated activities. RESULTS: The labrum in dysplastic hips supported 2.8-4.0 times more of the load transferred across the joint than in normal hips. Dysplastic hips did not have significantly different congruency in the primary load-bearing regions than normal hips, but were less congruent in some unloaded regions. Normal hips had larger cartilage contact stress than dysplastic hips in the few regions that had significant differences. CONCLUSIONS: The labrum in dysplastic hips has a far more significant role in hip mechanics than it does in normal hips. The dysplastic hip is neither less congruent than the normal hip, nor subjected to elevated cartilage contact stresses. This study supports the concept of an outside-in pathogenesis of OA in dysplastic hips and that the labrum in dysplastic hips should be preserved during surgery.

Finite element predictions of cartilage contact mechanics in hips with retroverted acetabula.

BACKGROUND: A contributory factor to hip osteoarthritis (OA) is abnormal cartilage mechanics. Acetabular retroversion, a version deformity of the acetabulum, has been postulated to cause OA via decreased posterior contact area and increased posterior contact stress. Although cartilage mechanics cannot be measured directly in vivo to evaluate the causes of OA, they can be predicted using finite element (FE) modeling. OBJECTIVE: The objective of this study was to compare cartilage contact mechanics between hips with normal and retroverted acetabula using subject-specific FE modeling. METHODS: Twenty subjects were recruited and imaged: 10 with normal acetabula and 10 with retroverted acetabula. FE models were constructed using a validated protocol. Walking, stair ascent, stair descent and rising from a chair were simulated. Acetabular cartilage contact stress and contact area were compared between groups. RESULTS: Retroverted acetabula had superomedial cartilage contact patterns, while normal acetabula had widely distributed cartilage contact patterns. In the posterolateral acetabulum, average contact stress and contact area during walking and stair descent were 2.6-7.6 times larger in normal than retroverted acetabula (P ≤ 0.017). Conversely, in the superomedial acetabulum, peak contact stress during walking was 1.2-1.6 times larger in retroverted than normal acetabula (P ≤ 0.044). Further differences varied by region and activity. CONCLUSIONS: This study demonstrated superomedial contact patterns in retroverted acetabula vs widely distributed contact patterns in normal acetabula. Smaller posterolateral contact stress in retroverted acetabula than in normal acetabula suggests that increased posterior contact stress alone may not be the link between retroversion and OA.

The transcription factors hypoxia-inducible factor 1alpha and Ets-1 colocalize in the hypoxic synovium of inflamed joints in adjuvant-induced arthritis.

OBJECTIVE: To determine the relationship between hypoxia and the expression of Ets-1 and hypoxia-inducible factor 1alpha (HIF-1alpha) in both normal and inflamed joints. Adjuvant-induced arthritis (AIA) was used as the model system, since it mirrors many aspects of the pathology of rheumatoid arthritis. METHODS: Adjuvant arthritis was induced in a group of 10 female Lewis rats. A second group of 10 uninjected female Lewis rats served as naive controls. When a maximum clinical joint score was achieved in the AIA group, all 20 rats were injected with the specific hypoxic cell marker Hypoxyprobe-1 and subsequently killed. Hypoxyprobe-1 adducts, Ets-1, and HIF-1alpha were localized in the joints of the hind feet from these groups using immunohistochemistry. RESULTS: Compared with the joints from control rats, inflamed joints contained markedly more cells with Hypoxyprobe-1 adduct immunoreactivity, Ets-1-immunoreactive nuclei, and nuclear immunoreactivity for both Ets-1 and HIF-1alpha. CONCLUSION: Our results demonstrate the presence of hypoxia in inflamed joints in this experimental model of arthritis. The colocalization of Ets-1 and HIF-1alpha in these hypoxic areas suggests that hypoxia may induce Ets-1 and HIF-1alpha expression during joint inflammation.

Primary total knee arthroplasty in the valgus knee: creating a balanced soft tissue envelope.

Lateral tissue releases in valgus total knee arthroplasty frequently produce asymmetric flexion-extension gaps and ligamentous instability. This study compared 2 lateral-release sequences and quantified the effects of sequential lateral capsular ligamentous structure release. One knee from 7 paired specimens was released according to a 4-step sequence: posterior cruciate ligament (PCL), ibiotibial tract (IT band), popliteus tendon/lateral collateral ligament (PT/LCL), and biceps femoris tendon. The contralateral knees were released according to a 5-step sequence: PCL, posterolateral capsule, IT band, PT, and LCL. After each release step, flexion and extension gaps were measured and recorded for the medial and lateral aspects. The 5-step sequence produced more symmetric flexion-extension gaps, whereas the absolute magnitudes of correction were lower than with the 4-step sequence. LCL sacrifice in both sequences produced marked lateral flexion-extension gap asymmetry.

Hip pain in the young adult: diagnosis and treatment of disorders of the acetabular labrum and acetabular dysplasia.

Hip pain in the young adult patient (ages, 17-35 years) is a diagnostic and therapeutic challenge for the orthopedic surgeon. The diagnostic and treatment algorithm for many causes of hip pain in the young adult-such as tumors and tumoral conditions, rheumatoid and degenerative arthritis, osseous necrosis, and the sequelae of congenital problems such as slipped capital femoral epiphysis and Legg-Calve Perthes--are well described and established. However, the diagnosis and treatment algorithm for disease processes, such as disorders of the acetabular labrum and dysplasia of the hip, are less clear. Advances in diagnostic radiology, particularly magnetic resonance arthrography, and advances in therapy, including the successful use of the Bernese periacetabular osteotomy and hip arthroscopy, have allowed for both timely diagnosis and appropriate treatment of these sources of hip pain in the young adult. The purpose of this review is to outline the diagnostic and treatment decision-making protocol for young adult patients with hip pain, and specifically to discuss the treatment of acetabular labral tears and dysplasia of the hip.

Triple innominate osteotomy in young adults for the treatment of acetabular dysplasia: a 9-year follow-up study.

Fifty patients who underwent 60 triple innominate osteotomies were reviewed radiographically and clinically using a modified Harris hip score (HHS). Average patient age was 26 years (range: 13-48 years). At average 9-year follow-up (range: 5-14 years), 12 (20%) hips had been converted to total hip arthroplasty (THA) and 4 (7%) hips had incapacitating pain. Sixteen (27%) hips were considered failures. Average modified HHS at final follow-up was 67 (range: 28-91). Forty-nine (98%) of 50 patients reported they would recommend the procedure to others in the same situation. Radiographically, there was significant improvement in the center-to-edge angle of Wiberg and the acetabular angle of Sharp. There also was a statistically significant relationship between failure of the osteotomy and severity of preexisting hip arthrosis as measured by the Tonnis criteria. The results demonstrate triple innominate osteotomy was effective in eliminating pain, but the fact that 27% of hips required or will require THA indicates results may deteriorate with time.

Total hip arthroplasty in young adults after failed triple innominate osteotomy.

This study compared the results of total hip arthroplasty (THA) in 11 patients with 13 hips who underwent THA after a failed triple innominate osteotomy (TIO) with an age-matched and sex-matched group of patients who underwent THA without prior TIO. The average age at the time of THA was 37 years (range, 16-50 years). The average follow-up of the patients who underwent THA for failed TIO was 36 months and for the control group was 28 months. One hip in each group underwent revision for dislocation. At final follow-up, the average Harris hip score in the study group was 76, whereas in the control group it was 88 (P <.05). The pain component of the Harris hip score in the study group averaged 32, whereas in the control group it averaged 40 (P <.05). Functional scores between the 2 groups were similar. Radiographically, there was no difference between the 2 groups. Estimated blood loss for the hips performed for failed TIO averaged 721 mL, whereas in the control group the estimated blood loss averaged 448 mL (P <.05). There was no difference in operative time. The results of this study indicated that although the radiographic results of THA after TIO are equivalent to THA without prior TIO, clinical results in terms of pain relief and the technical difficulty of THA are not equivalent to results in young adult patients who undergo THA without prior TIO.

The effect of femoral prosthesis design on cement strain in cemented total hip arthroplasty.

Finite element studies show that the highest cement stresses are located at the most proximal and distal ends of the prosthesis. In vitro biomechanical and histologic analyses of autopsy-retrieved cemented femoral components show these areas to be associated with cement-prosthesis debonding. In this study, cement strains were measured in 2 geometrically different femoral stems in paired cadaver femora: A straight, collared, moderately tapered stem (Centralign) was compared with an anatomically curved, collarless, dramatically tapered stem (Scientific Hip Prosthesis [SHP]). Results showed that the maximum strain and the overall strain profile differed between the 2 stems. The Centralign had peak strains located at the most proximal gauge positions, whereas the peak strains of the SHP were located around the middle of the femoral stem. Minimization of cement strain, especially at the crucial proximal and distal areas of the stem, by altering component design may be able to reduce cement-prosthesis debonding and improve clinical results.

A biomechanical analysis of internal fixation of complex tibial plateau fractures.

OBJECTIVE: To compare the mechanical stability of fixation of an unstable bicondylar tibial plateau fracture with several different fixation techniques in a cadaveric model. DESIGN: Randomized laboratory investigation using a simulated bicondylar tibial plateau fracture with metaphyseal-diaphyseal dissociation. SETTING: Complex tibial plateau fractures were instrumented and tested under ramp and cyclic loading conditions on a servohydraulic materials testing machine. INTERVENTION: Each tibia was instrumented sequentially with a lateral buttress plate, a lateral and a medial buttress plate, and a lateral buttress and an anteromedial antiglide plate for ramp load testing. For cyclic testing, one of the three constructs was used on each specimen. MAIN OUTCOME MEASUREMENTS: Vertical subsidence of the medial tibial plateau was measured in both ramp and cyclic loading in order to evaluate the three internal fixation techniques. RESULTS: No significant difference was measurable between the dual buttress construct and the lateral buttress/anteromedial antiglide construct. However, the lateral buttress plate alone provided significantly less stability. CONCLUSIONS: A lateral buttress plate with an anteromedial antiglide plate may provide equally effective fixation as compared with the dual buttress plating technique in complex tibial plateau fractures. This less invasive technique may also be associated with fewer complications due to the lack of soft tissue stripping that is required for its application.

Brachialis muscle entrapment in displaced supracondylar humerus fractures: a technique of closed reduction and report of initial results.

A retrospective review was conducted of 152 extension-type supracondylar humerus fractures in 151 children. Ninety-two (61%) of 152 of these fractures were displaced (Gartland type III). Initial irreducibility was present in 20 of the 92 displaced fractures. Brachialis muscle interposition was diagnosed by physical examination or intraoperative findings in 18 (90%) of the 20 initially irreducible fractures. Sixteen of the fractures with brachialis muscle interposition underwent an attempt at freeing the impaled proximal fragment by the described "milking maneuver." The maneuver was successful in 15 of the 16 patients and was followed by closed reduction and percutaneous pinning. Three of the remaining four cases required open reduction and pinning. We identify the incidence of initial irreducibility in displaced supracondylar humerus fractures, describe clinical findings suggestive of brachialis entrapment, and demonstrate the milking maneuver to be a valuable technique in the treatment of displaced supracondylar fractures with brachialis interposition.

The fate of well fixed cemented femoral components left in place at the time of revision of the acetabular component.

The results were reviewed for thirty-seven hips (thirty-five patients) in which a well fixed femoral component that originally had been implanted with use of a so-called first-generation cementing technique was subsequently left in place at the time of revision of the acetabular component without cement. The purpose of the study was to determine the rate of survival of the femoral component and the complications associated with revision of one side of the joint. The femoral components had been in situ for a mean duration of 102 months (range, twelve to 216 months) at the time of the revision of the acetabular component. At the time of follow-up after the revision of the acetabular component, one patient (one femoral component; 3 per cent) had died, twenty-seven femoral components (73 per cent) were in place and radiographically stable, one femoral component had been removed because of infection, six (16 per cent) had been revised because of aseptic loosening, and two (5 per cent) were definitely loose according to radiographic criteria. Excluding the failures and death, the mean duration of follow-up was sixty-five months (range, forty-eight to 121 months). The predicted survival of the femoral component after the revision of the acetabular component was 88 per cent (95 per cent confidence interval, 82 to 94 per cent) at forty-eight months and 78 per cent (95 per cent confidence interval, 67 to 89 per cent) at eighty-eight months. Dislocation occurred in three hips (8 per cent), and a trochanteric non-union occurred in five (14 per cent). The mean rate of linear polyethylene wear did not differ significantly (0.13 as compared with 0.12 millimeter per year; p = 0.74) from that for a comparable group of forty-nine hips that had had a revision of the femoral component without cement and had been followed for a similar duration. The data support the decision to retain a well fixed femoral component that has been implanted with a so-called first-generation cementing technique when the acetabular component subsequently needs a revision. The survival of the femoral component and the risk of associated complications do not appear to be appreciably altered by revision of the other side of the joint.

Revision total knee arthroplasty with a cemented posterior-stabilized or constrained condylar prosthesis: a minimum 3-year and average 5-year follow-up study.

The results of 57 revision total knee arthroplasties performed for aseptic failure between 1984 and 1992 with a cemented posterior-stabilized or constrained condylar prosthesis were reviewed at follow-up examinations at a minimum of 36 and an average of 62 months (range, 36-120 months). The reason for revision was aseptic loosening of 1 or both components in 32 knees (56%), instability in 16 knees (28%), polyethylene wear and osteolysis in 4 knees (7%), supracondylar femur fracture in 2 knees (4%), and a failed allograft, pain, and arthrofibrosis in 1 knee each (5% total). The average age of the patients at the time of the revision was 74 years (range, 38-90), and the original diagnosis for the majority of patients was osteoarthritis (74%). All of the revision prostheses were cemented posterior stabilized or constrained condylar-type implants. Bone deficiencies were grafted with cancellous allograft in contained defects and cortical allograft in noncontained defects. Five knees were reconstructed with allograft-prosthesis composites. The average modified Hospital for Special Surgery knee score improved from 49 to 82 (100 points possible) at final follow-up evaluation (P < 0.001). Seventy-nine percent of knees were graded as good or excellent. Kaplan-Meier survivorship analysis predicted 94%+/-6.2% survival at 40 months and 75%+/-25% at 99 months. There were 4 clinical failures, 3 of which were related to residual instability in patients with a posterior-stabilized prosthesis. Complications (3 knees) were exclusively related to the extensor mechanism. Radiographically, overall knee alignment improved from 0.3 degrees varus to 3.0 degrees valgus. Fifty-six percent of tibial components were placed in slight varus alignment. Radiolucent lines occurred in 33% of knees, but there were no complete or progressive radiolucencies. Radiolucent lines were more prevalent adjacent to press-fit intramedullary femoral stems compared with cemented stems (P < .02), but the difference did not correlate with clinical or radiographic failure. The median bone defect score, as proposed by the Knee Society Committee on Bone Defects, was significantly greater in knees that were revisions of a failed cemented total knee arthroplasty compared with revision of a failed cementless total knee arthroplasty (P = .02) but was not correlated with clinical or radiographic outcome (P > .05).

The bone-implant interface of femoral stems with non-circumferential porous coating.

UNLABELLED: A histological study was performed of the bone-implant interface of fifteen titanium-alloy femoral stems with porous coating limited to three proximal areas that did not cover the full circumference of the device. The specimens were obtained at autopsy from ten cadavera at a mean of forty-six months (range, one to eighty-nine months) after the implant had been inserted without acrylic cement. The volume fraction of bone within the porous spaces (the percentage of the porous space that was filled with bone) and the extent of bone ingrowth (the percentage of the porous-coated surface covered with in-grown bone that was more than one-half fiber-diameter deep, as measured from the outer surface of the porous coating), were determined with histomorphometric methods. Eleven of the fifteen stems had bone within the porous coating that was in continuity with the surrounding medullary bone. The mean volume fraction of bone ingrowth in these specimens was 26.9 per cent (range, 12.2 to 61.0 per cent), and the mean extent of bone ingrowth was 64.3 per cent (range, 28.6 to 95.2 per cent). Both of these parameters increased with time. In the other four stems, the bone lacked continuity with the surrounding trabecular bed. Two of these stems had a limited amount of bone within the porous coating, and two stems (from one patient) had no bone ingrowth. Periprosthetic membranes surrounded by a shell of trabecular bone covered the uncoated surfaces of the stems. The membranes of implants that had been in situ for eight months or more demonstrated polyethylene wear debris, and other particles generated at the level of the joint, within histiocytes throughout the length of the femoral stem. CLINICAL RELEVANCE: The findings in this study are relevant to the utilization and mechanisms of failure of femoral stems inserted without cement. Bone ingrowth and the resulting stability of the implant can be achieved with porous-coated stems. However, the extent of the surface that is porous-coated must be sufficient to prevent trabecular fracture as a secondary mechanism of loosening. Interruptions in the circumferential extent of the porous surface are associated with the formation of periprosthetic membranes, which provide a pathway for migration of particulate wear and corrosion products to the distal part of the stem. A circumferential coating may retard the access of particles and thus decrease the possibility of diaphyseal osteolysis.

Revision total hip arthroplasty without cement: subsidence of proximally porous-coated femoral components.

We prospectively studied the intermediate-term results of forty-nine revision total hip arthroplasties without cement that were performed because of aseptic loosening of a cemented femoral component in forty-five consecutive patients; the mean duration of follow-up was sixty-five months (range, forty-five to eighty-seven months). A curved, long-stem, titanium-alloy, non-circumferentially porous-coated femoral component was implanted in each hip. Preoperatively, a staging system was used to classify deficiencies of femoral bone stock according to the loss of cancellous or cortical bone in the metaphysis and diaphysis. Forty-one hips (84 per cent) had cortical or ectatic cavitary bone loss in the metaphysis. The mean Harris hip score significantly improved from 54 points preoperatively to 84 points at the time of the latest follow-up examination (p < 0.001). Twenty-seven patients (twenty-eight hips; 57 per cent) had at least two millimeters of subsidence of the femoral component during the first postoperative year. Eight patients (eight hips; 16 per cent) had no further progression of subsidence. Twenty-one patients (twenty-two hips; 45 per cent) had at least two millimeters of subsidence on two separate postoperative evaluations and therefore were considered to have progressive subsidence. Seventeen patients (nineteen hips; 39 per cent) had no measurable subsidence and were considered to have a stable femoral component. One of these seventeen patients had had a bilateral femoral revision and had progressive subsidence on one side. There was a positive trend for an association between subsidence and the degree of preoperative femoral bone deficiency (p = 0.10), but there was no association between subsidence and the fit of the prosthesis in the metaphysis and diaphysis or the fill of the canal of the femur (p > 0.50). There was no significant loss of bone in the hips with either a stable or a subsided femoral component (p > 0.50), and qualitative reconstitution of the cortex was noted in eleven (52 per cent) of the twenty-one most severely deficient (stage-III) femora. Survivorship analysis showed that, at seventy-two months, there was a 96 per cent chance of survival of the component (95 per cent confidence limits, 0.89 to 1.0) with revision as the end point but only a 37 per cent chance of survival (95 per cent confidence limits, 0.15 to 0.59) with revision or progressive subsidence as the end point.(ABSTRACT TRUNCATED AT 400 WORDS)

Compartment syndrome in the forearm following fractures of the radial head or neck in children.

A volar compartment syndrome of the forearm was identified following a minimally displaced or angulated fracture of the radial head or neck in three children. The fractures were due to a fall from a bed or from a standing height on an outstretched hand. All three patients had symptoms and signs that were consistent with elevated intracompartmental pressure in the forearm when they were first examined, twelve to twenty-four hours after the injury, and all were managed with an emergency fasciotomy of the forearm. The radial fracture was treated without reduction in the first patient, with manipulative closed reduction in the second patient, and with open reduction and stabilization with Kirschner wires in the third patient. All three patients had a full functional recovery.