Biomedical subjects

Sean Molloy

Publications and source records attributed to Sean Molloy.

12 recordsLinked to original sources

PubMed2005

Health outcome measures in the evaluation of total hip arthroplasties--a comparison between the Harris hip score and the Oxford hip score.

There has been an increasing need for the sensitive and reproducible measurement of the outcome after hip surgery. Numerous hip scoring systems, varying in their complexity and disease specificity, have been designed to achieve a measure of outcome-some rely ultimately on the judgement of the surgeon, whereas others rely on the patients' perceptions. The Oxford hip score (OHS) has been found to be easier to administer and achieves a much higher follow-up rate than that of the Harris hip score (HHS). Unfortunately, with the availability of numerous scoring systems and the publication of data in these systems, it has been difficult to compare results. Our aim was to compare the more widely used HHS to the shorter OHS. We followed 200 consecutive primary total hip arthroplasties (196 patients between January 1994 and May 1995) for an average of 5 years. All patients had a preoperative HHS recorded. At the 5-year review, assessment was made using OHS and the HHS. There were 115 hips that had full OHS and HHS available. The mean OHS was 19.1 (range 12-52, SD 9.5), and HHS was 89.4 (range 47-100, SD 13.3) at follow-up. The Spearman correlation showed good negative correlation between the 2 results (Spearman rank -0.712, P < .0001). The HHS vs OHS shows good correlation at 5 years. This is the first study to confirm that correlation persists for the OHS in the medium term. We include a classification of OHS of excellent (<19), good (19-26), fair (27-33), and poor (>33) outcomes which correlate well with the HHS. This study enables the case for the Oxford data with its easier analysis and higher compliance rate to be used more directly to compare studies that use the HHS.

Adult↗

PubMed2005

Interference Kirschner wires augment distal humeral fracture fixation in the elderly.

OBJECTIVES: This study was designed to compare the biomechanical stability of a two-plate distal humerus fixation with and without Kirschner-wire (K-wire) augmentation of supracondylar osteotomies. DESIGN: Ex vivo paired cadaveric study. SETTING: Biomechanical laboratory. MATERIALS: : Five pairs of fresh, elderly cadaveric humeri. INTERVENTION: Two 3.5-mm reconstruction plates were used to stabilize each humerus. This fixation model was selected solely to evaluate the effect of K-wire augmentation. Augmentation consisted of 2 K-wires placed in both the medial and lateral columns of the humerus to interdigitate with the plate screws. A posteriorly directed load was cyclically applied to the distal fragment for 5000 cycles or until failure, and osteotomy site motion was tracked optically. MAIN OUTCOME MEASUREMENTS: Fixation survival was defined as 5000 cycles or the number of cycles until osteotomy site motion reached >2 mm. RESULTS: K-wire augmented fixations survived significantly more cycles than did controls (4410 +/- 875 vs. 1114 +/- 2182, respectively; paired t test, P < 0.05). CONCLUSIONS: Augmentation with K-wires may decrease the incidence of loss of fixation in distal humeral fractures.

Age Factors↗

PubMed2005

Effect of cement volume and placement on mechanical-property restoration resulting from vertebroplasty.

BACKGROUND AND PURPOSE: Concern exists that vertebral bodies augmented with cement placed laterally may be at risk of collapse on the nonaugmented side. The purpose of the current study was to determine if placing the cement laterally rather than centrally resulted in risk of collapse on the nonaugmented side. METHODS: Vertebral bodies (L2-L5) were harvested from eight osteoporotic female cadaver spines. Simulated vertebral-body compression fractures were created and stabilized by injecting 3.5 or 7.0 mL of cement centrally or laterally. Vertebral bodies were recrushed to measure their augmented strength and stiffness. Anterior, posterior, left, and right lateral heights were measured initially, after augmentation, and after recompression. RESULTS: Lateral and central 3.5-mL injections of cement restored strength, whereas 7.0-mL injections significantly increased strength compared with initial values. The stiffness of vertebral bodies receiving central 3.5-mL injections was significantly less than it was initially, although the stiffness of bodies receiving 3.5-mL laterally was not significantly different from initial values. Initial and posttreatment stiffness values did not significantly differ in vertebral bodies receiving 7.0-mL, lateral or central injections. Vertebral heights did not significantly differ between the augmented and the final compression states in any location. Height loss between central and lateral injections did not differ significantly. CONCLUSION: Vertebral bodies in which cement is placed laterally do not appear to be at risk for collapse on the unaugmented side.

Aged↗

PubMed2004

Biomechanical comparison of kyphoplasty with different bone cements.

STUDY DESIGN: Ex vivo biomechanical study. OBJECTIVES: To compare the biomechanical properties of isolated, fractured, osteoporotic vertebral bodies after treatment by kyphoplasty with one of two cements: alpha-tri-calcium phosphate cement (Biopex-R; Mitsubishi Materials Corp., Tokyo, Japan) or polymethylmethacrylate (Simplex P; Stryker-Howmedica-Osteonics, Mahwah, NJ). SUMMARY OF BACKGROUND DATA: Kyphoplasty and vertebroplasty typically use polymethylmethacrylate cements for the treatment of osteoporotic compression fractures. Scant information exists regarding the use of alternative cements in kyphoplasty. METHODS: Simulated compression fractures were created in 24 vertebral bodies (T6-T9, L2-L5) harvested from three female cadavers. Vertebral bodies were assigned to one of two groups: kyphoplasty with Biopex-R or kyphoplasty with Simplex P. The kyphoplasty treatment consisted of inserting bone tamps bipedicularly into each vertebral body, inflating the tamp, and filling the created void with Biopex-R or Simplex P. Pretreatment and post-treatment heights were measured, and the repaired vertebral bodies were recompressed to determine posttreatment strength and stiffness values. Differences were checked for significance (P < 0.05) using a repeated-measures analysis of variance followed by Tukey's test. RESULTS: Kyphoplasty with Biopex-R restored strength in the lumbar and thoracic vertebral bodies. Kyphoplasty with Simplex P displayed significantly greater posttreatment strength than initial strength in the thoracic region. Vertebral bodies augmented with either cement were significantly less stiff than their initial conditions, except for the thoracic vertebrae treated with Simplex P, in which stiffness was restored. There was no significant difference in percentage of height restored between the cement treatments. CONCLUSIONS: Kyphoplasty with either cement restored initial strength. In general, stiffness was not restored.

Aged↗

PubMed2004

Ex vivo measurement of intravertebral pressure during vertebroplasty.

STUDY DESIGN: Ex vivo biomechanical study using cadaver vertebral bodies. OBJECTIVE.: To measure the increase in internal vertebral body pressure from cement injection during vertebroplasty. SUMMARY OF BACKGROUND DATA: Theoretically, the increased force required to inject polymerizing (viscous) cement into a vertebral body during vertebroplasty could produce a concomitant increase in intravertebral pressure and cause additional damage to the vertebral body. An alternative means of reducing intravertebral pressure during injection may be needed. METHODS: We placed 11-gauge cannulas bipedicularly in six vertebral bodies from each of two fresh female cadaver spines (one osteoporotic, one normal). One cannula served as the injection route; a manometer was connected to the other. After immersion of the spines in a saline bath, the vertebral bodies were injected with 10 mL of Simplex P cement by depressing the syringe plunger at a rate of 7 mm/sec using a materials testing machine. Static pressure was measured before and after injection. Peak pressure was measured during injection. Maximum pressure elevation was calculated as peak pressure minus initial static pressure. RESULTS: Maximum pressure elevation averaged (+/-SD) 9.4 +/- 8.5 mm Hg and 6.4 +/- 5.0 mm Hg in the osteoporotic and normal spines, respectively. In all cases (9 of 12) in which the pressure measurement system remained patent (i.e., not occluded by cement), postinjection pressure returned to the initial static pressure. CONCLUSION: The increase in intravertebral body pressure from cement injection during vertebroplasty is minimal. Alternative means of reducing intervertebral pressure before injection may not be needed.

Aged↗

PubMed2004

Biomechanical evaluation of intramedullary nail versus tension band fixation for transverse olecranon fractures.

OBJECTIVES: To compare the biomechanical stability of an alternative custom-designed intramedullary nail (IMN) fixation with that of traditional tension band wiring (TBW), the gold standard for stabilizing transverse olecranon fractures. DESIGN: Ex vivo biomechanical study. SETTING: Biomechanical laboratory. MATERIALS: Six pairs of elderly cadaver elbows. INTERVENTION: A simulated transverse olecranon fracture was created in each elbow after it had been denuded of most of its soft tissue. The right and left olecranons of each pair were alternately assigned to the IMN or TBW group. A tensile force was applied via the triceps tendon while the elbow was secured in 90 degree of flexion. MAIN OUTCOME MEASUREMENTS: Displacement at the simulated fracture segment was measured optically. Fixation failure was defined as >2 mm of fracture displacement. The differences in stiffness and maximum load to failure between the two treatments were analyzed for significance (P < 0.05) using a one-tailed paired t test. RESULTS: IMN fixation was significantly stiffer and stronger than TBW fixation. CONCLUSIONS: The locked IMN provided stronger and stiffer fixation than did TBW. Theoretically the IMN fixation would require less surgical exposure and would be expected to require fewer revisions than TBW fixation. IMN fixation warrants consideration as a clinical alternative to TBW.

Aged↗

PubMed2004

Is the Charnley evolution working? A five-year outcome study.

Two hundred consecutive primary total hip arthroplasties (196 patients) carried out between January 1994 and May 1995 using the Elite Plus cemented femoral components (DePuy International, Leeds, UK) were enrolled in a prospective study. Fifteen patients were lost to follow-up. The patients were evaluated clinically using the Harris Hip Score (HHS) and radiographically. The mean HHS was raised from 39.3 preoperatively to 89.6 at 5 years. Radiologically the mean femoral subsidence was 1.40 mm at 5 years. The mean annual rate of re-operation was 0.2%. There were no revisions for aseptic loosening. In the present series, the Elite Plus hip arthroplasty has produced clinical and radiological results, which are comparable with the Charnley hip at five years.

Adult↗

PubMed2003

The effect of vertebral body percentage fill on mechanical behavior during percutaneous vertebroplasty.

STUDY DESIGN: An ex vivo biomechanical study was conducted using osteoporotic cadaveric vertebral bodies. OBJECTIVE: To determine the relationship between the percentage of osteoporotic vertebral body volume filled with polymethylmethacrylate cement during percutaneous vertebroplasty and the percentage restoration of strength and stiffness. SUMMARY OF BACKGROUND DATA: A previous biomechanical study reported a weak relationship between the volume of cement injected and restoration of vertebral body strength and stiffness. Vertebral bodies vary considerably in size among regions and among spines, and the weak correlation may be attributed to the fact that the volume of vertebral bodies was not explicitly considered. METHODS: The volume of 120 vertebral bodies (T6-L5) harvested from 10 osteoporotic female cadaver spines was determined by Archimedean displacement. Compression fractures were experimentally created, and initial strength and stiffness were determined. The vertebral bodies were stabilized using bipedicular injections of 2-8 mL of cement and then recompressed, after which posttreatment strength and stiffness were measured. Linear regression was used to analyze the relationship between percentage of volume fill and percentage of restored stiffness and strength. RESULTS: The correlations between percentage of fill and restored strength and stiffness were weak: r2 = 0.21 and r2 = 0.27, respectively. On average, restoration of strength and stiffness required vertebral body cement fills of 16.2% and 29.8%, respectively. CONCLUSION: Strength and stiffness are weakly correlated with the percentage fill volume of cement injected during vertebroplasty.

Absorptiometry, Photon↗

PubMed2003

Temperature measurement during polymerization of polymethylmethacrylate cement used for vertebroplasty.

STUDY DESIGN: Ex vivo biomechanical study using osteoporotic cadaveric vertebral bodies. OBJECTIVE: To measure internal vertebral body temperature during polymerization of cements used for vertebroplasty. SUMMARY OF BACKGROUND DATA: Previous ex vivo studies have shown that temperature increases during cement polymerization were unlikely to cause thermal necrosis. METHODS: Twenty-four osteoporotic vertebral bodies were instrumented with thermocouples and injected with one of two cement volumes (6 or 10 mL) of one of two cements (Simplex P or modified Simplex P, Stryker-Howmedica-Osteonics, Kalamazoo, MI). Vertebral bodies were placed in a bath (37 C) and temperatures were measured for 15 minutes from the time the cement was initially mixed. RESULTS: In the vertebral bodies, peak temperatures at the anterior cortex ranged from 44 C to 113 C, those in the center ranged from 49 C to 112 C, and those at the spinal canal ranged from 39 C to 57 C. Dwell times at temperatures above 50 C at the anterior cortex ranged from 0 to 5.5 minutes, those in the center ranged from 0 to 8 minutes, and those at the spinal canal ranged from 0 to 2.5 minutes. CONCLUSION: Internal temperature elevation measured during cement polymerization was substantially higher than previously reported and may be sufficiently high to pose a risk of thermal necrosis.

Aged↗

PubMed2003

Biomechanical comparison of two fixation methods for first metatarsophalangeal joint arthrodesis.

PURPOSE: The aim of this study was to compare the mechanical stability of two methods of fixation for arthrodesis of the hallux metatarsophalangeal joint: 1. a technique using an intramedullary screw and 2. a standard technique using crossed interfragmentary compression screws. METHODOLOGY: The metatarsophalangeal joint was mechanically evaluated in cantilever bending using a servohydraulic testing machine. Differences in stiffness and strength parameters between the two techniques were checked for significance (P<0.05) using a paired t-test. RESULTS: Fixation provided by the intramedullary screw was stiffer and stronger than that from crossed compression screws. CONCLUSIONS: The stronger and stiffer intramedullary screw technique offers mechanical advantages over the crossed interfragmentary screw technique.

Aged↗

PubMed2003

Fifth metatarsal tuberosity fracture fixation: a biomechanical study.

This study tested the hypothesis that fixation of a fifth metatarsal tuberosity fracture with a lag screw that engages the intact medial cortex is biomechanically stronger than fixation with a long intramedullary screw (control). The right and left feet from 10 male cadavers were alternately assigned to the two fixation groups. After fracture reduction and fixation, each specimen was potted in acrylic cement and tested on a servohydraulic testing machine. The repairs were then distracted until failure by placing the peroneus brevis tendon under tension at a rate of 1 mm/s. The lag screw technique resulted in a significantly greater mean (+/- SD) load to failure (150 +/- 90 N) than did intramedullary screw fixation (70 +/- 60 N) (p < .05) and may offer a useful method of internal fixation of fifth metatarsal tuberosity fractures when surgical stabilization is indicated.

Aged↗

PubMed2002

Excision of an osteoid osteoma from the body of the axis through an anterior approach.

Osteoid osteoma is seen less commonly in the vertebral body than in the posterior elements of the spine. To the authors' knowledge, this is only the second reported case of an osteoid osteoma affecting the body of the axis. The patient described in this report presented with the classic symptomatology of pain and torticollis. Radiological imaging confirmed the diagnosis. A superior extension of the anterior Smith-Robinson approach, through the "window of access" described by Fasel, was used to excise this lesion. Following surgical excision, there was complete resolution of the presenting symptomatology and functionally the range of motion of the cervical spine returned to normal. We avoided instrumentation and C1-C2 fusion so that rotation of the cervical spine could be maintained. There were no signs of recurrence of the tumour within the 4-year follow-up period. It presented in a classic way but, despite this, it took 2 years from the onset of these symptoms to reach a definitive diagnosis. This osteoid osteoma was successfully excised through a superior extension of the anterior Smith-Robinson approach.

Adolescent↗