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Biomedical subjects

N P Thomas

Publications and source records attributed to N P Thomas.

At least 19 recordsLinked to original sources
PubMed2006

Combined anterior cruciate reconstruction and Oxford unicompartmental knee arthroplasty.

The options for treatment of the young active patient with isolated symptomatic osteoarthritis of the medial compartment and pre-existing deficiency of the anterior cruciate ligament are limited. The potential longevity of the implant and levels of activity of the patient may preclude total knee replacement, and tibial osteotomy and unicompartmental knee arthroplasty are unreliable because of the ligamentous instability. Unicompartmental knee arthroplasties tend to fail because of wear or tibial loosening resulting from eccentric loading. Therefore, we combined reconstruction of the anterior cruciate ligament with unicompartmental arthroplasty of the knee in 15 patients (ACLR group), and matched them with 15 patients who had undergone Oxford unicompartmental knee arthroplasty with an intact anterior cruciate ligament (ACLI group). The clinical and radiological data at a minimum of 2.5 years were compared for both groups. The groups were well matched for age, gender and length of follow-up and had no significant differences in their pre-operative scores. At the last follow-up, the mean outcome scores for both the ACLR and ACLI groups were high (Oxford knee scores of 46 (37 to 48) and 43 (38 to 46), respectively, objective Knee Society scores of 99 (95 to 100) and 94 (82 to 100), and functional Knee Society scores of 96 and 96 (both 85 to 100). One patient in the ACLR group needed revision to a total knee replacement because of infection. No patient in either group had radiological evidence of component loosening. The radiological study showed no difference in the pattern of tibial loading between the groups. The short-term clinical results of combined anterior cruciate ligament reconstruction and unicompartmental knee arthroplasty are excellent. The previous shortcomings of unicompartmental knee arthroplasty in the presence of deficiency of the anterior cruciate ligament appear to have been addressed with the combined procedure. This operation seems to be a viable treatment option for young active patients with symptomatic arthritis of the medial compartment, in whom the anterior cruciate ligament has been ruptured.

Adult↗
PubMed2006

Smoking and reconstruction of the anterior cruciate ligament.

We sought to determine whether smoking affected the outcome of reconstruction of the anterior cruciate ligament. We analysed the results of 66 smokers (group 1 with a mean follow-up of 5.67 years (1.1 to 12.7)) and 238 non-smokers (group 2 with a mean follow-up of 6.61 years (1.2 to 11.5)), who were statistically similar in age, gender, graft type, fixation and associated meniscal and chondral pathology. The assessment was performed using the International Knee Documentation Committee form and serial cruciometer readings. Poor outcomes were reported in group 1 for the mean subjective International Knee Documentation Committee score (p < 0.001), the frequency (p = 0.005) and intensity (p = 0.005) of pain, a side-to-side difference in knee laxity (p = 0.001) and the use of a four-strand hamstring graft (p = 0.015). Patients in group 1 were also less likely to return to their original level of pre-injury sport (p = 0.003) and had an overall worse final 7 International Knee Documentation Committee grade score (p = 0.007). Despite the well-known negative effects of smoking on tissue healing, the association with an inferior outcome after reconstruction of the anterior cruciate ligament has not previously been described and should be included in the pre-operative counselling of patients undergoing the procedure.

Adolescent↗
PubMed2005

Influence of surface geometry and the cam-post mechanism on the kinematics of total knee replacement.

Abnormal sagittal kinematics after total knee replacement (TKR) can adversely affect functional outcome. Two important determinants of knee kinematics are component geometry and the presence or absence of a posterior-stabilising mechanism (cam-post). We investigated the influence of these variables by comparing the kinematics of a TKR with a polyradial femur with a single radius design, both with and without a cam-post mechanism. We assessed 55 patients, subdivided into four groups, who had undergone a TKR one year earlier by using an established fluoroscopy protocol in order to examine their kinematics in vivo. The kinematic profile was obtained by measuring the patellar tendon angle through the functional knee flexion range (0 degrees to 90 degrees ) and the results compared with 14 normal knees. All designs of TKR had abnormal sagittal kinematics compared with the normal knee. There was a significant (p < 0.05) difference between those of the two TKRs near to full extension. The presence of the cam-post mechanism did not influence the kinematics for either TKR design. These differences suggest that surface geometry is a stronger determinant of kinematics than the presence or absence of a cam-post mechanism for these two designs. This may be because the cam-post mechanism is ineffective.

Aged↗
PubMed2005

Tensile strength of the medial patellofemoral ligament before and after repair or reconstruction.

The tensile strength of the medial patellofemoral ligament (MPFL), and of surgical procedures which reconstitute it, are unknown. Ten fresh cadaver knees were prepared by isolating the patella, leaving only the MPFL as its attachment to the medial femoral condyle. The MPFL was either repaired by using a Kessler suture or reconstructed using either bone anchors or one of two tendon grafting techniques. The tensile strength and the displacement to peak force of the MPFL were then measured using an Instron materials-testing machine. The MPFL was found to have a mean tensile strength of 208 N (SD 90) at 26 mm (SD 7) of displacement. The strengths of the other techniques were: sutures alone, 37 N (SD 27); bone anchors plus sutures, 142 N (SD 39); blind-tunnel tendon graft, 126 N (SD 21); and through-tunnel tendon graft, 195 N (SD 66). The last was not significantly weaker than the MPFL itself.

Aged↗
PubMed2004

When is a meniscal cyst not a meniscal cyst?

Two patients are presented where lesions adjacent to the joint line of the knee were diagnosed clinically and on magnetic resonance imaging (MRI) as meniscal cysts. No concomitant meniscal tears were seen, and the MRI signal was not completely homogenous. The diagnostic imaging influenced the surgical management in a manner inappropriate for the definitive diagnoses of fibromyxoid sarcoma and monophasic synovial sarcoma. Not all cysts produce a purely homogenous signal on MRI due to haemorrhage or high protein content fluid, and not all meniscal cysts are associated with a meniscal tear. In the absence of a meniscal tear and with mixed signal on MRI we advise caution in the diagnosis of a meniscal cyst and advocate shared management with either orthopaedic or radiological colleagues with a special interest in oncology to obtain a tissue diagnosis before definitive treatment.

Adolescent↗
PubMed2003

The effect of screw length and position on fixation of four-stranded hamstring grafts for anterior cruciate ligament reconstruction.

The aim of this study was to examine interference screw fixation of four strand hamstring grafts for anterior cruciate ligament reconstruction in vitro. Bovine tibiae and cannon tendons were used. Screws were introduced from 'outside-in'. The tendons were loaded cyclically to 150 N to simulate walking and 450 N to simulate jogging. Slippage of the tendon from the anchorage was recorded after 100, 300 and 1000 cycles. Cortico-cancellous and cancellous only fixations were compared using a 7-mm screw in an 8-mm tunnel with a 7-mm graft. The effect of screw length was studied by comparing 8 x 25 and 8 x 45 mm screws. Graft slippage with cancellous only fixation was significantly greater than with cortico-cancellous screw fixation (P 0.105), the longer screws gave more consistent behaviour. We concluded that the screw should be placed so that its head engages the cortex, while increasing screw length within cancellous bone did not significantly improve graft fixation. Cyclical load testing reflects the repetitive forces imposed in the early post-operative period following hamstring anterior cruciate ligament reconstruction and is important for the evaluation of graft fixations.

Animals↗
PubMed2003

Anatomy and biomechanics of the medial patellofemoral ligament.

The medial patellofemoral ligament (MPFL) is a band of retinacular tissue connecting the femoral medial epicondyle to the medial edge of the patella. The MPFL is approximately 55 mm long, and its width has been reported to range from 3 to 30 mm. The MPFL is overlaid by the distal part of vastus medialis obliquus to a variable extent, and fibres of MPFL merge into the deep aspect of the muscle. Despite the MPFL being very thin, it had a mean tensile strength of 208 N, and has been reported to be the primary passive restraint to patellar lateral displacement. Lateral patellar displacement tests in vitro showed that the patella subluxed most easily at 20 degrees knee flexion. The contribution of the MPFL to resisting patellar lateral subluxation was greatest in the extended knee. This finding was linked to the retinaculae being tightest in full knee extension, and slackening with flexion.

Biomechanical Phenomena↗
PubMed2001

A comparison of bone remodelling around hydroxyapatite-coated, porous-coated and grit-blasted hip replacements retrieved at post-mortem.

We investigated the implant-bone interface around one design of femoral stem, proximally coated with either a plasma-sprayed porous coating (plain porous) or a hydroxyapatite porous coating (porous HA), or which had been grit-blasted (Interlok). Of 165 patients implanted with a Bimetric hip hemiarthroplasty (Biomet, Bridgend, UK) specimens were retrieved from 58 at post-mortem. We estimated ingrowth and attachment of bone to the surface of the implant in 21 of these, eight plain porous, seven porous HA and six Interlok, using image analysis and light morphometric techniques. The amount of HA coating was also quantified. There was significantly more ingrowth (p = 0.012) and attachment of bone (p < 0.05) to the porous HA surface (mean bone ingrowth 29.093 +/- 2.019%; mean bone attachment 37.287 +/- 2.489%) than to the plain porous surface (mean bone ingrowth 21.762 +/- 2.068%; mean bone attachment 18.9411 +/- 1.971%). There was no significant difference in attachment between the plain porous and Interlok surfaces. Bone grew more evenly over the surface of the HA coating whereas on the porous surface, bone ingrowth and attachment occurred more on the distal and medial parts of the coated surface. No significant differences in the volume of HA were found with the passage of time. This study shows that HA coating increases the amount of ingrowth and attachment of bone and leads to a more even distribution of bone over the surface of the implant. This may have implications in reducing stress shielding and limiting osteolysis induced by wear particles.

Aged↗
PubMed2000

Taking the advanced knee arthroscopic surgery course to Singapore.

The Advanced Knee Arthroscopic Surgery course was first organised in 1995 under the joint auspices of the British Association for Surgery of the Knee and The Royal College of Surgeons of England. This is a two-day course in advanced knee arthroscopic techniques, with lectures, videos and extensive practical sessions. The approach is very much hands-on, using cadavers together with sawbones and model knees. Use is also made of the specimens in the Anatomical Museum of the College. Instruction is given in anterior cruciate ligament reconstruction, meniscal repair and posterior cruciate with posterolateral ligament reconstruction. Since 1995 the course has been held on seven occasions and has been attended by over 100 senior trainees and consultants.

Arthroscopy↗
PubMed1997

A prospective trial of local versus general anaesthesia for arthroscopic surgery of the knee.

We set out to determine if arthroscopic knee surgery was acceptable to patients and their surgeon when carried out using a local anaesthetic infiltration technique. Patients awaiting arthroscopy were randomly allocated to have either a local or a general anaesthetic. The same surgeon (NPT) carried out all the procedures. The demographic profile was similar in the two groups, as were the diagnosis and the surgical procedures. The only difference between the two groups was that those performed under local anaesthesia did not have a limb tourniquet inflated. The time spent in the theatre suite was similar in each group. This did not include the recovery time in the general anaesthetic group. The duration of the operation was longer in the local anaesthetic group (P = 0.05). A simple 0 to 10 scoring system indicated that patients preferred a local anaesthetic but the surgeon preferred to have the patient asleep (P > 0.05). Those having a local anaesthetic required less physiotherapy (P = 0.025) and more of them returned to work and sport earlier (P = 0.05). We attributed this to not having sustained pressure-induced tissue damage to the thigh muscle as they did not have a tourniquet inflated. We had a 4% failure rate in the local anaesthetic group. Arthroscopic surgery is already a well-established day case procedure and our findings have a financial implication (a saving of 25 pounds per case) as well as identifying a safer technique in the medically unfit. Unfortunately, this technique is not suitable for the investigation and treatment of all knee problems. There are certain constraints, viz the very anxious patient, acute problems, children, larger arthroscopic procedures and the inability to perform an examination under anaesthetic but, overall, it is a useful and effective way of performing a common surgical procedure.

Adolescent↗
PubMed1994

Reconstruction nailing for subtrochanteric fractures in the Pagetic femur.

Three cases of subtrochanteric fractures in patients with Paget's disease are presented which were treated by closed intramedullary nailing using the Russel-Taylor reconstruction nail. In one case with severe deformity of the femur, diaphyseal osteotomy was required to enable implant insertion. All fractures (including the osteotomy) united. There were no operative or long-term complications and no implant failures. The reconstruction nail is ideal for such cases and has technical and biomechanical advantages over other implants.

Aged↗
PubMed1990

Comparative analysis of four types of synthetic anterior cruciate ligament replacement in the goat: in vivo histological and mechanical findings.

The in vivo biological and mechanical performance of four artificial anterior cruciate ligament replacements, available for clinical use, was examined in the goat over a period of 2 yr. The prostheses used in the study were manufactured from polytetrafluoroethylene, Dacron or a composite of Dacron and carbon fibres. Histologically, no device was found to perform adequately both intraosseously and intra-articularly. The breaking load for each device immediately after insertion and after 12 month was found to be lower than that of the normal anterior cruciate ligament. All devices were found to have partially or completely ruptured intra-articularly after 2 yr.

Animals↗
PubMed1989

Brace treatment of Colles' fracture.

Twenty patients with Colles' fractures were treated with a functional brace that allows wrist motion. The result was compared with a similar group of patients treated with a plaster cast. Dorsal displacement of the fracture was less and wrist function was better in the brace group. Swelling of the hand during the early stages was observed in the brace group; and because this may necessitate brace adjustment, increased medical supervision is necessary for this period.

Adult↗
PubMed1987

Prosthetic anterior cruciate ligaments in the rabbit. A comparison of four types of replacement.

Four types of prosthetic replacement for the anterior cruciate ligament (carbon fibre, carbon fibre and Dacron composite, Dacron alone and bovine xenograft) were assessed at three, six and 12 months after implantation in the knees of New Zealand white rabbits. The synovium and both intra-articular and intra-osseous portions of the ligaments were examined macroscopically, by light microscopy and by scanning electron microscopy. All the knees showed mild synovitis, and there was no significant growth into the intra-articular part of any ligament. Carbon fibre and xenograft did not appear to be suitable materials in this animal model. The composite ligament showed short-term ingrowth of fibrous tissue only into the periphery of the sheath in its intra-osseous portion, whereas the Dacron ligament showed progressive fibrous tissue ingrowth with some bony incorporation of its outer fibres.

Animals↗
PubMed1986

Craniocervical instability treated by contoured loop fixation.

Rigid posterior fixation of the skull to the third, fourth and fifth cervical vertebrae was achieved in three patients who, as a result of operation, had gross instability of the craniocervical junction. An anatomically contoured steel loop was secured to the occiput via small burr holes and to the vertebrae by sublaminar wiring. This technique has the advantage over bone grafting, either alone or with cement, in that it affords rigid stabilisation, allows early mobilisation and may contribute to eventual bony fusion.

Adult↗