Accuracy of Bone Resection in MAKO Total Knee Robotic-Assisted Surgery.

Accurate component positioning and planning is vital to prevent malalignment of total knee arthroplasty (TKA) as malalignment is associated with an increased rate of polyethylene wear and revision arthroplasty. The MAKO total knee robotic arm-assisted surgery (Stryker, Kalamazoo, MI) uses a preoperative computed tomography scan of the patient's knee and three-dimensional planning to size and orientate implants prior to bone resection. The aim of this study was to determine the accuracy of the MAKO Total Knee system in achieving the preoperative plan for bone resection and final limb coronal alignment. A series of 45 consecutive cases was performed using the MAKO Total Knee system and Triathlon Total Knee implant (Stryker) between April 2018 and May 2019. The difference between what was planned and what was achieved for bone resection and coronal limb alignment was calculated. A total of 37 patients had their data captured using the MAKO system software. Mean difference from the plan for distal femoral cuts was 0.38mm (0.32) deep/proud, anterior femoral cuts 0.44mm (0.27) deep/proud and tibial cuts 0.37mm (0.30) deep/proud. In total, 99 out of 105 (94.29%) of bone resections were within 1mm of the plan. Mean absolute difference in final limb coronal alignment was 0.78° (0.78), with 78.13% being ≤1.00° of the plan, and 100% being ≤3.00° of the plan. The accuracy in achieving preoperatively planned bone resection and final limb coronal alignment using the MAKO Total Knee system is high. Future research is planned to look at whether this is associated with decreased rates of polyethylene wear and revision arthroplasty.

Early Results of the ARPE Arthroplasty Versus Trapeziectomy for the Treatment of Thumb Carpometacarpal Joint Osteoarthritis.

BACKGROUND: Thumb carpometacarpal joint arthroplasty for osteoarthritis may hold advantages over trapeziectomy by preserving range of motion, whilst providing stability and preventing thumb shortening. METHODS: We compare functional and satisfaction outcomes scores, radiological shortening and complication rates between patients treated with trapeziectomy and those receiving the ARPE thumb CMCJ arthroplasty. RESULTS: Seventy-five trapeziectomies and one hundred and ten ARPE arthroplasties were performed over the study period. Both treatments resulted in significant improvements in functional scores. When matching patients according to pre-operative function, patients receiving the ARPE arthroplasty had better post-operative function (Quick DASH: trapeziectomy = 25.1, ARPE = 16.8). More patients receiving the ARPE arthroplasty were satisfied with their treatment (trapeziectomy = 7.8/10, ARPE = 8.7/10) and would have the same treatment again (trapeziectomy = 76%, ARPE = 89%). The ARPE also resulted in less thumb shortening. However the ARPE arthroplasty is associated with a higher complication rate, with 14% of patients requiring further surgery at a mean of 2 years follow up (95% implant survival). CONCLUSIONS: Both trapeziectomy and the ARPE CMCJ arthroplasty are effective treatment options for thumb CMCJ osteoarthritis. Arthroplasty may offer potential advantages in terms of post-operative function and patient satisfaction. However the risk of complications and requirement for further surgery is greater and must be carefully considered during patient selection and pre-operative counselling.

Revision of unicompartmental knee arthroplasty versus primary total knee arthroplasty.

The risk of revision following unicompartmental arthroplasty (UKA) is greater compared with primary total knee arthroplasty (TKA). Some surgeons report that UKA revision is straightforward with outcomes comparable to TKA. We reviewed all Oxford medial UKAs and TKAs performed at our institution over a five year period. Patient reported outcomes were compared between revised UKAs, successful UKAs and primary TKAs. Out of 546 Oxford medial UKAs, twenty-nine (5.3%) were revised at a mean of 25months. The commonest indications for revision were aseptic loosening and progression of osteoarthritis. Ten patients (34%) required augments, stemmed implants or bone grafts. Outcomes following revision were poorer than those following successful UKA and primary TKA, and were a consequence of poor pre-operative function rather than the complexity of surgery.

The effect of ankle joint immobilization on lower limb venous flow.

BACKGROUND: Below-knee cast immobilization is associated with an increased risk of developing deep vein thrombosis secondary to venous stasis. We investigated the effect of weight-bearing in a below-knee cast or pneumatic walking boot on lower limb venous blood flow. METHODS: Duplex ultrasonography was used to measure venous blood flow in the popliteal vein of 10 healthy volunteers. Venous blood flow was measured while at rest, ambulating non-weight-bearing, partial weight-bearing, and full weight-bearing. Measurements were performed without ankle joint immobilization, with the ankle immobilized in a neutral cast, and with the ankle immobilized in a pneumatic walking boot in both neutral and equinus. RESULTS: There was no significant reduction in venous blood flow measurements between full weight-bearing without ankle joint immobilization and full weight-bearing in a neutral cast or neutral pneumatic walking boot. However, venous blood flow was reduced when partial weight-bearing (50%) and when full weight-bearing in a pneumatic walking boot in equinus. CONCLUSION: These results demonstrate that venous blood flow returned to normal levels when the subjects were permitted to fully bear weight in below-knee casts or walking boots, provided that the ankle joint was not in equinus. CLINICAL RELEVANCE: Weight-bearing status and ankle joint position should be appreciated during decisions for the provision of chemical thromboprophylaxis.

Human evolution and tears of the rotator cuff.

PURPOSE: Humans differ from other great ape species in their propensity to develop tears of the rotator cuff. The aim of this study was to compare the anatomical risk factors for subacromial impingement and rotator cuff tears amongst the great apes and to determine which features may be accentuated in humans and therefore play a more significant role in disease aetiology. METHODS: Orthogonal digital photographs of 22 human, 17 gorilla, 13 chimpanzee and 12 orangutan dry bone scapula specimens oriented in the glenoid plane were taken. Anatomical measurements were preformed using a calibrated digital image technique and the results scaled according to scapula vertebral border length. RESULTS: Of the ten anatomical features associated with subacromial impingement and rotator cuff tears in humans, none were shown to be accentuated and significantly different to the other species studied. However the human supraspinatus fossa was shown to be significantly smaller. CONCLUSIONS: These results indicate that an alternative primary aetiological factor for rotator cuff tears must exist. A reduction in the size of the supraspinatus fossa in human scapulae suggests that structural insufficiency of the supraspinatus or a change in rotator cuff force vectors could play a role.

Can local administration of tranexamic acid during total knee arthroplasty reduce blood loss and transfusion requirements in the absence of surgical drains?

Blood transfusions are frequently required following total knee arthroplasty. Tranexamic acid (TXA) inhibits fibrinolysis and has been shown to reduce blood loss and transfusion requirements when delivered intravenously. Topical and intra-articular applications directly target bleeding sites whilst limiting systemic uptake and theoretically reduce the risk of thromboembolic complications. However, in the absence of surgical drains, which increase post-operative blood loss, the efficacy of these techniques for reducing transfusion requirements is unclear. Our aim was to determine if locally administered tranexamic acid during total knee arthroplasty could reduce both blood loss and transfusion requirements in the absence of surgical drains. A retrospective review of 248 patients treated with primary unilateral cemented total knee arthroplasty was performed. Patients treated after January 2011 received topical and intra-articular tranexamic acid at the end of the procedure (n = 136). A second group of consecutive patients treated before this period acted as historical controls (n = 112). Patient groups were equivalent in terms of age, gender and ASA grade. There was a significant reduction in mean blood loss of 246 ml between the groups (p < 0.01). In addition, the requirement for post-operative allogenic blood transfusion was significantly reduced from 15.5 to 5.4 % after introduction of the tranexamic acid regimen (p = 0.02). This is the largest patient cohort reviewed to measure the efficacy of locally administered tranexamic acid during total knee arthroplasty and demonstrates that this is an effective technique for reducing both blood loss and transfusion requirements in the absence of surgical drains.

Distal humerus cortical strains following total elbow arthroplasty.

The aseptic loosening of total elbow replacements is a serious complication resulting in significant patient morbidity. It is thought to occur secondary to stress shielding of the distal humeral cortex by the stiff stem of the implant. Some total elbow prostheses incorporate an anterior flange intended to improve implant stability and peri-articular load transfer in an attempt to reduce this effect However, few studies have directly assessed the changes in cortical strains following total elbow arthroplasty or the biomechanical advantage of the anterior flange design. A regular and a long flange Coonrad-Morrey total elbow prosthesis were implanted into six Sawbone synthetic humeri. The constructs were subjected to physiological loads in axial compression (500 N), antero-posterior bending (50 N) and antero-posterior compression with condylar supports (300 N). Digital image correlation was used to measure the distal antero-lateral cortical strains and the results compared with those of whole Sawbones that had been tested in the same way. Significant stress shielding was demonstrated over the distal humeral cortex following prosthesis implantation during axial compression. In contrast, cortical strains increased following prosthesis implantation during antero-posterior compression with condylar supports. The increase in cortical strains following total elbow arthroplasty may help to maintain the integrity of the anterior cortex offering additional stability for implants with an anterior flange. These results are important for the development of future total elbow prosthesis designs and indicate that simulating the action of the forearm muscles is essential when evaluating changes in strain about the distal humerus in vitro.

Heparin-induced thrombocytopenia following hip and knee arthroplasty.

Until recently, both the British Society for Haematology and American College of Chest Physicians recommended platelet monitoring in all surgical patients receiving prophylactic low molecular weight heparin (LMWH) for the early diagnosis of heparin-induced thrombocytopenia (HIT). These guidelines were reversed in 2012 based upon an analysis considering resource expenditure, assay result timeframes, and complications relating to HIT treatment. However, there are no large studies reviewing lower limb arthroplasty patients on an individual basis to determine the incidence of HIT in this patient group. This study investigated 10 797 patients who underwent primary hip or knee arthroplasty with LMWH prophylaxis over a 5 years period. 32·6% of patients (n = 3515) had platelet counts recorded up to 14 d postoperatively with 13 patients (0·37%) developing thrombocytopenia. Platelet counts recovered spontaneously in five patients, and two patients had other identifiable causes. Only one of the remaining six patients developed thrombosis indicating an incidence of HIT-related thrombosis of 0·03%. The potential for identifying HIT with platelet monitoring in patients receiving LMWH prophylaxis is low and therefore routine monitoring for HIT is not justified.

Regulation of SHP-1 tyrosine phosphatase in human platelets by serine phosphorylation at its C terminus.

SHP-1 is a Src homology 2 (SH2) domain-containing tyrosine phosphatase that plays an essential role in negative regulation of immune cell activity. We describe here a new model for regulation of SHP-1 involving phosphorylation of its C-terminal Ser591 by associated protein kinase Calpha. In human platelets, SHP-1 was found to constitutively associate with its substrate Vav1 and, through its SH2 domains, with protein kinase Calpha. Upon activation of either PAR1 or PAR4 thrombin receptors, the association between the three proteins was retained, and Vav1 became phosphorylated on tyrosine and SHP-1 became phosphorylated on Ser591. Phosphorylation of SHP-1 was mediated by protein kinase C and negatively regulated the activity of SHP-1 as demonstrated by a decrease in the in vitro ability of SHP-1 to dephosphorylate Vav1 on tyrosine. Protein kinase Calpha therefore critically and negatively regulates SHP-1 function, forming part of a mechanism to retain SHP-1 in a basal active state through interaction with its SH2 domains, and phosphorylating its C-terminal Ser591 upon cellular activation leading to inhibition of SHP-1 activity and an increase in the tyrosine phosphorylation status of its substrates.