Stem diameter and micromotion of press fit radial head prosthesis: a biomechanical study

Demographics, Indications, and Revision Rates for Radial Head Arthroplasty: Analysis of Data from the Australian Orthopaedic Association National Joint Replacement Registry

BACKGROUND

Population-level data from national arthroplasty registries enable the use and outcomes of arthroplasty procedures to be monitored over time. This study aimed to describe the demographics, indications, and outcomes (up to 15 years) for radial head arthroplasty (RHA) procedures in Australia, as well as the factors associated with an increased likelihood of revision.

METHODS

Individual-level deidentified data on demographics and surgery characteristics, including revision surgery, were obtained from the Australian Orthopaedic Association National Joint Replacement Registry for all primary isolated RHA procedures that had been performed from 2007 to 2021. The probability of prosthesis survival was determined using Kaplan-Meier estimates. Cox proportional hazards models were used to calculate hazard ratios (HRs) for revision.

RESULTS

A total of 3,457 primary RHAs were performed during the study period (mean follow-up, 5.6 years; range, 0 to 15 years). The mean age at the time of RHA was 53 years, with female predominance (n = 2,009, 58%). The most common indication for RHA was fracture or dislocation (n = 3,166, 92%), followed by osteoarthritis (n = 232, 7%). The radial head prostheses that were most commonly used were monopolar (n = 3,378, 98%) with a modular design (n = 3,442, 99.6%) and cementless fixation (n = 3,387, 98%). Both metallic and nonmetallic prostheses were used (52% and 48%, respectively). Of the total cohort, 160 revisions (5%) were performed during the 15-year period; most revisions occurred in the first 5 years. The most common revision indication was prosthesis loosening (n = 62, 39%), and 54% of the revisions (n = 87) involved a change of the radial component. In multivariable analysis, primary procedures for osteoarthritis (HR, 1.65; 95% confidence interval [CI], 1.01 to 2.70) or "other" indications (e.g., inflammatory arthritis, osteonecrosis, or tumor) were revised more frequently (HR, 3.68; 95% CI, 1.14 to 11.91) than procedures for fracture or dislocation. Procedures with nonmetallic prostheses had higher rates of revision (HR, 1.61; 95% CI, 1.17 to 2.22) than those with metallic prostheses.

CONCLUSIONS

Trauma remained the most prevalent indication for RHA in Australia from 2007 to 2021. Encouragingly, revision rates were low, most notably for RHA that had been performed for fracture or dislocation. The likelihood of revision was highest for RHA procedures performed for osteoarthritis and for an indication other than osteoarthritis or trauma. Nonmetallic prostheses had a higher rate of revision than metallic prostheses.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Short- to midterm outcomes of 139 pyrocarbon monopolar radial head arthroplasties

BACKGROUND

The MoPyc radial head arthroplasty (RHA) is a monopolar implant with a pyrocarbon head that obtains rigid fixation via controlled expansion of the titanium stem. The aim of this study was to evaluate the short-term to midterm outcomes of MoPyc RHA.

MATERIALS AND METHODS

Between 2002 and 2021, 139 MoPyc RHA were implanted in 139 patients with a RH fracture. The mean follow-up was 5.9 years ± 3.5 (range 1-16). Range of motion, mean Mayo Elbow Performance Score (MEPS), Quick Disabilities of the Arm, Shoulder and Hand score, visual analog scale (VAS), radiographic outcome, and reason for failure were recorded.

RESULTS

The mean MEP, Quick Disabilities of the Arm, Shoulder and Hand, and VAS scores were 89.1 ± 2.2 (range, 45-100), 17.5 ± 16.7 (range, 0-78), and 0.8 ± 1.6 (range, 0-50), respectively. Stress shielding (SS) and osteolysis around the stem were identified in 92 (66%) and 20 (14%) patients. A total of 47 (29%) patients experienced at least 1 complication and 29 (21%) of them required re-intervention. Persistent stiffness (n = 12; 9%) was the most common complication. No painful loosening was noted. Osteolysis around the stem, presence of an autoexpanding stem, and overstuffing were associated with a lower MEPS and an increase in VAS (P < .05). SS was associated with an increase in MEPS (adjusted beta coefficients= 6.92; P < .001) and lower VAS (adjusted beta coefficients= -0.69; P = .016). The autoexpending stem increased the likelihood of SS after RHA (adjusted odds ratio = 1.49; P = .001).

CONCLUSIONS

A well-fixed MoPyc RHA provided satisfactory short to midterm outcomes, without painful loosening. However, the autoexpanding stem system was associated with poorer functional outcomes and increased the likelihood of SS.

Physical, functional and personal variables affecting shoulder complaints in healthcare workers

BACKGROUND

Work-related shoulder disorders adversely affect the quality of life and lead to increased costs related to decreased productivity and injury treatment. Therefore, understanding the relationship between strength, upper extremity function and work ability contributes to the development of interventions aimed to improve the well-being of healthcare workers.

OBJECTIVE

Correlate shoulder abduction and handgrip strength with upper extremity function and work ability in healthcare workers with shoulder complaints.

METHODS

67 workers with shoulder pain in the last year were assessed by Disability of Arm, Shoulder and Hand (QuickDASH), Work Ability Index (WAI), isokinetic shoulder strength and isometric handgrip strength dynamometers. Data were analysed with Spearman's Correlation Coefficient (ρ= 0.05), SPSS 20.0®.

RESULTS

52% males, mean age 48.4 years, 42% physically active, most administrative and general services workers. Low correlation between handgrip strength and QuickDASH (r=-0.359; p = 0.004); low correlation between handgrip strength and WAI (r = 0.359; p = 0.003) and between shoulder abduction strength and the QuickDASH (r = -0.267; p = 0.049); no significant correlation between shoulder abduction strength and WAI (r = 0.001; p = 0.997).

CONCLUSIONS

Handgrip and shoulder abduction strength were inversely associated with upper extremity dysfunction. Shoulder abduction strength was associated with work ability. The inclusion of strength assessment in workers is important to guide strategies to prevent musculoskeletal disorders.

Radial neck osteolysis after radial head replacement: Functional impact and risk factors

INTRODUCTION

Onset of radial neck osteolysis (RNO) has been reported after radial head replacement (RHR), but data are sparse regarding impact and risk factors. We therefore conducted a retrospective study, 1) to quantify RNO after RHR, 2) to assess clinical and radiological impact, and 3) to identify risk factors.

HYPOTHESIS

RNO prevalence is high, but functional impact is limited.

MATERIAL AND METHOD

A single-center retrospective study included all patients undergoing RHR for acute radial head fracture between 2008 and 2017: 53 patients, with a mean age of 53.8±15.7 years [range, 21-85 years]. At a minimum 2 years' follow-up, patients were assessed clinically on joint range of motion and Mayo Elbow Performance Score (MEPS) and radiologically on standard radiographs. Associations between RNO and various parameters were assessed.

RESULTS

At a mean 46.7±19.8 months' follow-up [range, 24-84 months], RNO was found in 54.7% of cases (29/53), with mean 4.0 ±2.8mm distal extension [range, 1.2-13.4mm], corresponding to 13.4±7.3% of stem height [range, 2.7-27.7%]. RNO at last follow-up was not significantly associated with reduced flexion-extension (121.9° versus 114.0°; p=0.11), pronation-supination (152.6° versus 138.3°; p=0.25) or MEPS (84.7 versus 84.8; p=0.97), or with higher rates of postoperative complications (11/29 (37.9%) versus 7/24 (29.2%); p=0.782) or surgical revision (11/29 (37.9%) versus 10/24 (41.7%); p=0.503). RNO was significantly associated with cementless fixation (19/29 (65.5%) versus 7/24 (29.2%); p=0.01), unipolar prosthesis (21/29 (72.4%) versus 7/24 (29.2%); p=0.002), high filling-ratio, whether proximal (88% versus 77%; p=0.002), middle (84% versus 75%; p=0.007) or distal (69% versus 59%; p=0.032), and shorter radial stem (33.2mm versus 46.3mm; p=0.011). No demographic parameters showed significant association with RNO at last follow-up.

CONCLUSION

RNO was frequent after RHR, but without clinical or radiological impact in the present series. The risk factors identified here argue for involvement of stress shielding.

LEVEL OF EVIDENCE

IV, cohort study.

Anatomic Monopolar Press-fit Radial Head Arthroplasty; High Rate of Loosening at Mid-Term Follow Up

Introduction

Radial head arthroplasty (RHA) is used for the management of unstable or unreconstructable injuries of the radial head. Our aim was to investigate clinical and radiographic outcomes in patients treated with the Acumed anatomic radial head press-fit system for trauma.

Methods

Clinical and radiographic assessment of RHAs undertaken for trauma with minimum 2-year follow-up.

Results

16 consecutive patients, mean age 53 (21-82) and 66 month ± 27 (26-122) clinical follow-up were included. There were marked radiographic changes with 11/16 showing periprosthetic lucent lines and 13/16 showing subcollar osteolysis. Radiographic changes occurred early post-surgery. Stem loosening was associated with larger cantilever quotients (0.47 vs 0.38, p  =  0.004). Overall survivability was 81.2%, with 3 RHAs removed. Clinical outcomes for the retained RHAs were acceptable with mean flexion 134°, extension deficit of 10°, pronation of 82°, and supination of 73°. Mean VAS scores were 8.5 ±  14.4, QuickDASH 13.8 ±  18.9, Mayo Elbow Performance Scores were 91.5 ±  12.5 with no poor scores.

Conclusion

Mid-term clinical functional outcomes following the Acumed anatomic RHA are acceptable in most cases. However, in view of the extensive periprosthetic lucencies and surgical removal due to loosening, patients should be cautioned when consented for implantation of the prosthesis, especially if a large collar is anticipated.

Early aseptic loosening of a press-fit radial head prosthesis - A case series of 6 patients

OBJECTIVE

Radial head arthroplasty (RHA) is the principal treatment option for comminuted radial head (RH) fractures. Here, we present six cases of failed RHA using a modular monopolar press-fit RHA that was subsequently withdrawn from the market because it was associated with a high incidence of loosening.

METHODS

We retrospectively collected data from six patients who had received Radial Head Prothesis System^TM at our centre between July 2015 and June 2016. The average follow-up was 40 months.

RESULTS

Aseptic loosening of the stem affected five (83%) of the six RHA. Four of these were symptomatic and RHA removal was performed. For these patients, the pain subsided and their elbow range of motion (ROM) improved.

CONCLUSION

While the ideal design for an RHA is still debatable, RHA is an efficient treatment option that restores elbow stability and function after a comminuted RH fracture. Importantly, removal of the prosthesis is an effective remedy following RHA associated elbow pain and decreased ROM.

Early to midterm radiographic loosening of the press fit radial head prosthesis

BACKGROUND

Radiographic loosening is frequently seen around the radial head (RH) implant. The hypothesis of this study was that radiographic loosening will be more frequent in patients in which the RH prosthesis was implanted due to elbow trauma leading to instability that required lateral collateral ligament repair (LCL).

MATERIALS AND METHODS

A retrospective review of the patients who had RH implantation between 2012 and 2019 was performed. Evaluation included evidence of radiographic loosening, stress shielding, formation of heterotopic ossification, and rate of removal of the implant. Range of motion of the elbow at the latest follow up was also recorded.

RESULTS

At a mean follow up of 18 months (range 1.4 - 80) eight out of 25 patients had radiographic loosening around the implant. The radial head implant was removed in 8 patients (in 3 due to painful radiographic loosening, in 4 due pain without radiographic loosening and in 1 due to infection). Radiographic loosening around the RH implant had no association with LCL repair (p=0.18) or future removal of implant (p=0.18) or the diagnosis of Monteggia lesion (p=0.68). In addition, removal of the RH implant had no association with prior LCL repair (p=0.60) or the diagnosis of Monteggia lesion (p=0.15). Stress shielding was seen in 5 patients and was of no clinical significance. Heterotopic ossification was seen in 12 patients and was classified as Class I in 3, IIA in 3, IIC in 6, according to the Hastings Classification. The average flexion-extension arc was 23° to 130°, and average pronation-supination was 76° to 69°.

CONCLUSION

One third of the patients had radiographic loosening around the RH implant at a mean follow up of 18 months. Pain with or without radiographic loosening were the main reasons for removal of the implant. No associations were found between the development of radiographic loosening and LCL repair at the time of RH replacement. Limitations of this study are: (a) the retrospective design (b). the small sample size and the possibility of a type II statistical error.

Assessment of the primary stability of revision tibial trays augmented with a cementless sleeve in AORI Type III defects

BACKGROUND

Previous studies have evaluated the initial stability of uncemented tibial components in revision total knee replacement (rTKR) in the presence of an Anderson Orthopaedic Research Institute (AORI) Type II tibial defect. This study sought to evaluate similar metrics in the severe Type III (AORI TIII) defects with combined uncemented stem and sleeve fixation, specifically, the effect of varying the stem's length and tibial canal engagement upon stability and bone strain.

METHOD

Finite element models generated from the CT scans of 4 tibias with Type III defects were used to investigate the primary stability, in terms of the bone-implant composite peak micromotion (CPM) and microstrains (CPS), achieved after virtual implantations with and without stems.

RESULTS

A stemless rTKR had increased metaphyseal CPM and CPS compared to all stemmed implants. Significant area of the bone supporting the stemless rTKR had CPS greater than bone yield (7000 με). Short engaging stems (≤150 mm construct length), could not achieve reliable engagement in the diaphysis (canal fill ≤ 50%), leading to insufficient reduction of CPS (≥5000 με). Longer engaging stems (170-220 mm construct length), were able to reliably engage the diaphysis (fill ratio ≥ 75%) resulting in CPS ≤ 5000 με. Although, non-engaging stems resulted in increased CPM and CPS compared to engaging stems, long non-engaging stems (170-220 mm construct) appeared to provide additional stability to the rTKR compared to stemless rTKR.

CONCLUSION

The results indicate a likely correlation between uncemented stem engagement and metaphyseal CPS in Type III defects. Excessive strain within the supporting metaphyseal bone is likely to lead to rTKR migration and loosening.

Pyrocarbon unipolar radial head prosthesis: clinical and radiologic outcomes at long-term follow-up

BACKGROUND

Several studies have already reported good short-term results with a pyrocarbon unipolar radial head prosthesis (Pyc-uRHP). The aim was to evaluate the evolution from mid- to long-term clinical and radiographic outcomes of a Pyc-uRHP.

METHODS

This was a retrospective, single-center study. We followed up all the patients who underwent Pyc-uRHP surgery in our original study at 2 years of follow-up (52 patients), reaching a minimum of 7 years of clinical and radiologic follow-up. This study included 26 patients who underwent a clinical examination assessing mobility, the Mayo Elbow Performance Score, and the visual analog scale score and radiologic evaluation with anteroposterior and profile radiographs at a mean follow-up of 110 months (range, 78-162 months). The radiologic study analyzed signs of proximal osteolysis, stem loosening, capitellar wear, and humeroulnar osteoarthritis.

RESULTS

No patients required revision. Eight patients required reoperation: coronoid screw removal in 1 and arthrolysis for stiffness in 7. The mean time to reoperation was 11 months. The mean Mayo Elbow Performance Score at last follow-up was 96 ± 9 (of 100), with a pain score of 42 ± 7 (of 45), mobility score of 19 ± 2 (of 20), stability score of 10 (of 10), and function score of 25 (of 25). Comparison with clinical data from the mid-term delay did not reveal any significant difference. All patients presented with proximal osteolysis around the neck but without progression. No stem loosening was noted. The rates of humeroulnar osteoarthritis (12% at mid-term vs. 80% at last follow-up, P < .0001) and capitellar lesions (34% at mid-term vs. 80% at last follow-up, P = .001) increased significantly.

CONCLUSION

We have shown that a Pyc-uRHP at 9 years' follow-up provided stable and satisfactory clinical results. Osteolysis of the radial neck was always present but it did not evolve, and no stem loosening was noted. Finally, we have shown a clear worsening of radiologic humeroulnar osteoarthritis and capitellar lesions that remained asymptomatic.

AI-Enabled Efficient and Safe Food Supply Chain

This paper provides a review of an emerging field in the food processing sector, referring to efficient and safe food supply chains, ’from farm to fork’, as enabled by Artificial Intelligence (AI). The field is of great significance from economic, food safety and public health points of views. The paper focuses on effective food production, food maintenance energy management and food retail packaging labeling control, using recent advances in machine learning. Appropriate deep neural architectures are adopted and used for this purpose, including Fully Convolutional Networks, Long Short-Term Memories and Recurrent Neural Networks, Auto-Encoders and Attention mechanisms, Latent Variable extraction and clustering, as well as Domain Adaptation. Three experimental studies are presented, illustrating the ability of these AI methodologies to produce state-of-the-art performance in the whole food supply chain. In particular, these concern: (i) predicting plant growth and tomato yield in greenhouses, thus matching food production to market needs and reducing food waste or food unavailability; (ii) optimizing energy consumption across large networks of food retail refrigeration systems, through optimal selection of systems that can be shut-down and through prediction of the respective food de-freezing times, during peaks of power demand load; (iii) optical recognition and verification of food consumption expiry date in automatic inspection of retail packaged food, thus ensuring safety of food and people’s health.

Midterm outcomes of 146 EVOLVE Proline modular radial head prostheses: a systematic review

INTRODUCTION

The EVOLVE implant (Wright Medical Technology, Arlington, TN, USA) is a modular loose-fitting radial head prosthesis. The primary objective was to synthesize all available literature investigating the midterm clinical outcomes of the EVOLVE implant.

MATERIALS AND METHODS

An electronic literature search in Pubmed/Medline, Scopus, EMBASE, and Cochrane library was performed querying for studies published in 2000-2017. Articles describing clinical and radiographical outcomes as well as reoperation were included. Outcomes of interest included range of motion, Mayo Elbow Performance Score, Disabilities of the Arm Shoulder and Hand, radiographic outcome, and reason for reoperation.

RESULTS

A total of five articles consisting of 146 patients with EVOLVE implants were included. Mean patient age was 57.4 years (range 22-84), and 43.8% were males (n = 64). Mean follow-up was 4.8 years (range 1-14). Mean Mayo Elbow Performance Score and Disabilities of the Arm Shoulder and Hand score were 87.6 (range 30-100) and 18.9 (range 0-82), respectively. Midterm clinical results were good or excellent (Mayo Elbow Performance Score > 74) in 94 patients. Reoperation was observed in 12 patients, with implant revision required in 2 patients. The primary reason for reoperation was persistent stiffness (n = 9).

CONCLUSION

Midterm outcomes of EVOLVE radial head prosthesis are satisfactory, and associated complication rates are low. Loose-fit implant method appears to be a reliable approach to avoid failure of radial head prosthesis by painful loosening.

Acute radial head replacement with bipolar prostheses: midterm results

In irreparable radial head fractures, especially if primary stabilizers of the elbow are damaged, the prosthetic replacement prevents instability and stiffness. Concerns have arisen over the use of bipolar press-fit prostheses due to the frequent finding of osteolysis and the risk of instability if compared to monopolar implants. Our aim was to assess midterm clinical and radiological outcomes of bipolar implants and the influence of osteolysis on proximal pain. Seventeen patients with irreparable fractures of the radial head, treated in acute with the same prosthetic model (rHEAD recon SBI/Stryker) between January 2015 and December 2018, were enrolled. Clinical assessment was performed using MEPS and DASH scores; a radiographic study was done to identify heterotopic ossifications and periprosthetic osteolysis. Outcomes at the last follow-up, according to MEPS, were excellent in 10 cases, good in 5 and fair in 2; none of the patients had severe pain or instability. In 3 cases, it was necessary to remove the implant, mainly because of early loosening. Radiological findings of osteolysis were detected in 9 cases, but no statistical correlation was found with MEPS and proximal pain. The use of bipolar implants is reliable if an accurate repair of ligament tears is performed and provides a good stability. Nevertheless, the risk of early aseptic loosening in uncemented implants is not negligible, and the follow-up of the patient must be strict. Late osteolysis does not seem to have clinical relevance, but further prospective studies are necessary to clarify this topic.

Indications and Clinical Results of Radial Head Replacement: Has Anything Changed?

Radial head fractures are common injuries comprising 1/3 of the fractures about the elbow. As a secondary valgus stabilizer of the elbow, radial head fractures can compromise elbow stability leading to long-term pain, dysfunction, and degenerative change. Furthermore, radial head fractures can be accompanied by associated injuries including ligamentous lesions that can further exacerbate elbow instability, leading to long-term sequelae. As fixation principles and technology have evolved, so has the ability to render surgical treatment for these fractures. In general, minimally displaced and some displaced fractures may be treated nonoperatively with early motion. Fractures with a block to rotation and displaced fragments with 3 or fewer fragments may be treated with open reduction and internal fixation. Comminuted fractures or those with greater than 3 fragments may be successfully treated with radial head replacement. Associated elbow instability will also influence treatment decisions.

Stem Length and Neck Resection on Fixation Strength of Press-Fit Radial Head Prosthesis: An In Vitro Model

PURPOSE

Various radial head prosthesis designs are currently in use. Few studies compare different prosthetic designs. We hypothesized that increasing a cementless implant stem's length would reduce stem-bone micromotion, with both short and long neck cuts. We also hypothesized that a minimum stem length might be required for the initial fixation strength of a press-fit implant.

METHODS

In 16 fresh-frozen cadaveric elbows (8 pairs), the radial head and neck were cut either 10 or 21 mm below the top of the head. Modular cementless stems were inserted and sequentially lengthened in 5-mm increments. Micromotion under eccentric loading was tested after each incremental change.

RESULTS

Incremental lengthening of the prosthetic stem and the amount of neck resection (10-mm cut vs 21-mm cut) both had a significant effect on micromotion. After a 10-mm radial head-neck resection, we observed a significant decrease in micromotion with stem lengths of 25 mm or greater, whereas with 21 mm of neck resection there was no further reduction in micromotion with increased stem length. These differences can be explained, at least in part, by the concept of the cantilever quotient: the ratio of the head-neck length outside the bone to the total length of the implant.

CONCLUSIONS

The length of the stem affects the initial stability of press-fit radial head prostheses when the level of head and neck resection is at the minimum (ie, 10 mm) for currently available prosthetic designs. At this resection level, stems 25 mm or greater had significantly higher initial stability, but all stem lengths tested had mean micromotion values within the threshold for bone ingrowth.

CLINICAL RELEVANCE

The length of a radial head prosthetic stem affects the initial stability of press-fit radial head prostheses when the level of head and neck resection is at the minimum (ie, 10 mm) for currently available prosthetic designs.

Metallic Press-fit Radial Head Replacement for Radial Head Fractures

This study evaluated the clinical and radiographic results of patients who sustained nonreconstructible radial head fractures that subsequently were treated with a metallic press-fit radial head prosthesis (RHP). Nine patients with comminuted radial head fractures were treated with a metallic press-fit RHP; mean follow-up was 38.7 months. The radial head fracture was acute in 6 patients (group A) and chronic in 3 patients (group B). Functional evaluation was assessed using the Mayo Elbow Performance Score (MEPS) and Disabilities of the Arm, Shoulder and Hand (DASH) Questionnaire. Radiographs were assessed for loosening, radiocapitellar alignment, osteolysis of the radial neck, lucency, periarticular ossifications, and ulnohumeral degeneration. Average flexion and flexion contracture were 133° and 5°, respectively. Average supination and pronation angles were 70° and 73°, respectively. Mean MEPS was 90 (range, 70-100), and elbow performance was excellent in 4 patients, good in 4 patients, and fair in 1 patient. Mean DASH score was 21.9 (range, 0-61). Flexion contracture, forearm rotation arc, and MEPS score were better and the complication rate was lower in group A compared with group B. Centering of the stem was observed on both anteroposterior and lateral radiographs in 6 patients. Lucent lines around the prostheses, stress shielding under the neck of the radius, and ectopic ossification occurred in 5 patients. Three patients had osteoarthritis. Elbow stiffness and ulnar impaction syndrome occurred in 2 patients but only after placement of a secondary RHP. Satisfactory outcomes were obtained using a metallic press-fit RHP for nonreconstructible radial head fractures. [Orthopedics. 2019; 42(6):e545-e551.].

Short to midterm outcomes of one hundred and seventy one MoPyC radial head prostheses: meta-analysis

BACKGROUND

The MoPyC implant is an uncemented long-stemmed radial head prosthesis that obtains primary press-fit fixation via controlled expansion of the stem. Current literature regarding MoPyC implants appears promising; however, sample sizes in these studies are small. Our primary objective was to evaluate the short- to midterm clinical outcomes of a large sample of the MoPyC prostheses. The secondary objective was to determine the reasons for failure of the MoPyC devices.

METHODS

Four electronic databases were queried for literature published between January 2000 and March 2017. Articles describing clinical and radiographic outcomes as well as reasons for reoperation were included. A meta-analysis was performed to obtain range of motion, mean Mayo Elbow Performance score (MEPS), radiographic outcome, and reason for failure.

RESULTS

A total of five articles describing 171 patients (82 males) with MoPyC implants were included. Mean patient age and follow-up were 52 years (18-79) and 3.1 years (1-9), respectively. Midterm clinical results were good or excellent (MEPS > 74) in 157 patients. Overall complication rate was low (n = 22), while periprosthetic osteolysis was reported in 78 patients. Nineteen patients returned to the operating room, with implant revision being required in ten patients. The two primary reasons for failure were (intra-)prosthetic dislocation (n = 8) followed by stiffness (n = 7); no painful loosening was described.

CONCLUSION

Short- to midterm outcomes of MoPyC prostheses are satisfactory and complications associated are low. The use of stem auto-expansion as a mode of obtaining primary fixation in radial head arthroplasty appears to be an effective solution for reducing the risk of painful loosening.

The effect of a radial neck notch on press-fit stem stability: a biomechanical study on 7 cadavers

BACKGROUND

Minimal micromotion is necessary for osteointegration of cementless radial head prostheses. When radial head fractures extend longitudinally, where the neck cut for prosthetic replacement should be made is uncertain. We hypothesized that complete resection of the notched portion of a radial neck confers no advantage in initial stability compared with not resecting the defect and inserting the implant into a notched radial neck.

MATERIALS AND METHODS

The radii of 7 cadavers underwent radial head resection and implantation with a 25-mm-long press-fit radial head stem. Before implantation, a 5-mm-long notch that was less than 1-mm wide was made in the radial neck. After the stem-bone micromotion was recorded, the proximal 5 mm of radial neck, incorporating the entire notch, was cut away, the stem was inserted 5 mm further, and the resulting micromotion was recorded.

RESULTS

The mean micromotion measured in the presence of a cortical notch was 51 ± 6 µm. After the neck was circumferentially cut and the stem was advanced, the micromotion (46 ± 9 µm) was not statistically significantly different.

DISCUSSION

Initial stability of an adequately sized cementless stem in the presence of a 5-mm-long cortical notch was well within the threshold needed for bone ingrowth (<100 µm). In addition, there was no reduction of micromotion after the notch-containing portion of the radial neck was resected and the stem was advanced. Making a neck cut distal to a 5-mm-long, 1-mm-wide cortical notch does not confer added stability. Thus, surgeons can preserve bone stock and avoid an aggressive neck cut.

The minimum follow-up required for radial head arthroplasty: a meta-analysis

AIMS

The primary aim of this study was to define the standard minimum follow-up required to produce a reliable estimate of the rate of re-operation after radial head arthroplasty (RHA). The secondary objective was to define the leading reasons for re-operation.

MATERIALS AND METHODS

Four electronic databases, between January 2000 and March 2017 were searched. Articles reporting reasons for re-operation (Group I) and results (Group II) after RHA were included. In Group I, a meta-analysis was performed to obtain the standard minimum follow-up, the mean time to re-operation and the reason for failure. In Group II, the minimum follow-up for each study was compared with the standard minimum follow-up.

RESULTS

A total of 40 studies were analysed: three were Group I and included 80 implants and 37 were Group II and included 1192 implants. In Group I, the mean time to re-operation was 1.37 years (0 to 11.25), the standard minimum follow-up was 3.25 years; painful loosening was the main indication for re-operation. In Group II, 33 Group II articles (89.2%) reported a minimum follow-up of < 3.25 years.

CONCLUSION

The literature does not provide a reliable estimate of the rate of re-operation after RHA. The reproducibility of results would be improved by using a minimum follow-up of three years combined with a consensus of the definition of the reasons for failure after RHA. Cite this article: Bone Joint J 2017;99-B:1561-70.

Radial head prosthesis: surgical tips and tricks

Radial head prostheses (RHP) have been developed to decrease the complications rate following a radial head resection surgery. The aim of the RHP is to replicate the physiological radiocapitellar tracking, reproducing the mechanical function of the native radial head: to stabilize the elbow and to shear the forces passing through the elbow along with the other stabilizers. The currently used RHP models try to achieve this target with three different prosthesis' strategies: (a) loose fit stem, (b) bipolar radial head or (c) anatomical radial head. Even if the radial head fixation is the preferred technique in every possible case and the resection can be still considered a possible option, in the last years there has been a growing worldwide consensus in using the radial head replacement in patients with unfixable radial head fractures, especially if associated with complex elbow instability. However, complications after a RHP are not uncommon, and their rate is raising as long as the implants number are increasing. The main difficulties are due to the implantation technique that needs to be performed with the same attention and precision used for the replacement of all the other joints, and to the concurrent treatment of the associated lesions. A personalized postoperative rehabilitation program is essential for obtaining good results and decreasing the complications rate. Concern exists for the young age of the patients that often require a RHP: personal experience and literature analysis suggest that if the clinical and radiographic results are positive after a 6-12-month follow-up, good outcomes can be also expected at a medium- or long-term follow-up.

Tight-fitting radial head prosthesis: does stem size help prevent painful loosening?

INTRODUCTION

The most common reason for removal of well-fixed radial head prostheses is painful loosening. We hypothesised that short-stemmed prostheses, used for radial head arthroplasty, are not associated with an increased risk of implant loosening.

METHODS

From 2002 to 2014, 65 patients were enrolled in a retrospective single-centre study. The radial head prostheses were classified as having either a long (30-mm) or short (16- to 22-mm) stem. The long-stemmed implants comprised 30 GUEPAR® DePuy Synthes (West Chester, PA, USA) and 20 Evolutive® Aston Medical (Saint-Etienne, France) devices; the short-stemmed implants comprised nine RECON and six STANDARD rHead® SBI-Stryker (Morrisville, PA, USA) devices. At last follow-up, clinical (range of motion, Disabilities of the Arm, Shoulder, and Hand score, Mayo Elbow Performance score) and radiographic (osteolysis) outcomes were assessed.

RESULTS

At a mean follow-up of 76.78 months (24-141), the rate of painful loosening [6 (40%) vs 8 (16%), p = 0.047] and osteolysis [12 (80%) vs 23 (46%), p = 0.02] were significantly higher in patients with short-stemmed versus long-stemmed implants. Despite the significant difference in loosening between stems as groups, individual stem length was not determined.

CONCLUSIONS

Tight-fitting implants with short stems are more prone to painful loosening.

Mid-term outcomes of 77 modular radial head prostheses

AIMS

Radial head arthroplasty (RHA) may be used in the treatment of non-reconstructable radial head fractures. The aim of this study was to evaluate the mid-term clinical and radiographic results of RHA.

PATIENTS AND METHODS

Between 2002 and 2014, 77 RHAs were implanted in 54 men and 23 women with either acute injuries (54) or with traumatic sequelae (23) of a fracture of the radial head. Four designs of RHA were used, including the Guepar (Small Bone Innovations (SBi)/Stryker; 36), Evolutive (Aston Medical; 24), rHead RECON (SBi/Stryker; ten) or rHead STANDARD (SBi/Stryker; 7) prostheses. The mean follow-up was 74.0 months (standard deviation (sd) 38.6; 24 to 141). The indication for further surgery, range of movement, mean Mayo Elbow Performance (MEP) score, quick Disabilities of the Arm, Shoulder and Hand (quickDASH) score, osteolysis and positioning of the implant were also assessed according to the design, and acute or delayed use.

RESULTS

The mean MEP and quickDASH scores were 90.2 (sd 14; 45 to 100), and 14.0 points (sd 12; 1.2 to 52.5), respectively. There were no significant differences between RHA performed in acute or delayed fashion. There were 30 re-operations (19 with, and 11 without removal of the implant) during the first three post-operative years. Painful loosening was the primary indication for removal in 14 patients. Short-stemmed prostheses (16 mm to 22 mm in length) were also associated with an increased risk of painful loosening (odds ratio 3.54 (1.02 to 12.2), p = 0.045). Radiocapitellar instability was the primary indication for re-operation with retention of the implant (5). The overall survival of the RHA, free from re-operation, was 60.8% (sd 5.7%) at ten years.

CONCLUSION

Bipolar and press-fit RHA gives unsatisfactory mid-term outcomes in the treatment of acute fractures of the radial head or their sequelae. The outcome may vary according to the design of the implant. The rate of re-operation during the first three years is predictive of the long-term survival in tight-fitting RHAs. Cite this article: Bone Joint J 2017;99-B1197-1203.

Radial head prosthesis: results overview

Background/purpose

Radial head replacement is frequently used in treatment of radial head fractures or sequela. Impossibility to restore a correct anatomy, acute elbow traumatic instability and failure of osteosynthesis hardware are the most common indications. The authors describe their case studies and results on the implantation of various radial head prostheses.

Materials

Between June 2005 and June 2016, 28 radial head prostheses were implanted in the same number of patients with an average follow-up of 49 months (6–104). Indications for implantation were: Mason type III and IV radial head fractures and post-traumatic arthritis due to failure of previous treatments. Monopolar prostheses were used and were press-fit implanted via Kaplan’s lateral access and Kocher’s anconeus approach to the humeroradial joint. At the follow-up, assessments were made of the pain, according to the visual analogic scale, range of motion (ROM), stability and functionality according to the Mayo Elbow Performance Score, presence of osteolysis and mobilization during radiography tests, personal satisfaction of the patients, Disabilities of the Arm, Shoulder and Hand and Patient-Rated Wrist Evaluation outcomes measurements.

Results

At the follow-up, we recorded an average level of pain of 1.8 in patients under acute treatments for radial head fractures and a marked reduction in the remaining cases from 6.7 to 2.1. ROM was found on average to be 107° of flexion–extension and 159° of pronosupination. Personal satisfaction was good–excellent in 23 cases. There was no case of infection; removal of the implant was necessary in three cases due to mobilization of the stem and oversized implants. In six cases, bone resorption was seen at the level of the prosthetic collar and it was in all cases asymptomatic.

Conclusions

The results of this study suggest that the use of prostheses, if well positioned, is a valid solution in the treatment of secondary arthritis and fractures of the radial head with poor prognosis, with good results in the reduction of pain, recovery of movement and improved quality of life.

Retrospective cohort study on radial head replacements comparing results between smooth and porous stem designs

BACKGROUND

When necessary, radial head integrity after a fracture can be re-created by the use of a radial head arthroplasty if the radial head is judged irreparable. The purpose of this study was to compare the clinical and radiographic outcomes of metal modular radial head replacements with a smooth vs. a porous stem.

METHODS

A retrospective cohort study of radial head replacements performed in the first 4 weeks after a trauma in an adult patient at our institution between 2000 and 2014 was completed. Patients were divided into 2 groups: a porous stem group (ExploR; Biomet Orthopedics, Warsaw, IN, USA) and a smooth stem group (EVOLVE; Wright Medical Group, Memphis, TN, USA). Primary outcomes were the Disabilities of the Arm, Shoulder, and Hand and Mayo Elbow Performance Index scores. Secondary outcomes were the visual analog scale score for pain, range of motion, grip strength, and radiographic evaluations.

RESULTS

Of the 80 eligible patients, 57 agreed to participate (porous stem group, 36; smooth stem group, 21). Demographic data were similar between the 2 groups. Average follow-up was 6.3 years. Average Disabilities of the Arm, Shoulder, and Hand and Mayo Elbow Performance Index scores were similar between the 2 groups. Porous implants were more prone to osteolysis (64.3% vs. 23.5%; P = .01) and were associated with a greater loss of elbow flexion (6° vs. 1°; P = .02). The porous stem group showed a tendency toward more overstuffing (24.0% vs. 5.9%; P = .21).

CONCLUSION

Our results reveal that outcomes between smooth and porous stem metal modular radial head implants are equivalent. However, the smooth stem implant may represent the preferred option as it is associated with a lower rate of complications.

Impacts of 3D bone-to- implant contact and implant diameter on primary stability of dental implant

BACKGROUND/PURPOSE

This study investigated the effects of three three-dimensional (3D) bone-to-implant contact (BIC) parameters-potential BIC area (pBICA), BIC area (BICA), and 3D BIC percentage (3D BIC%; defined as BICA divided by pBICA)-in relation to the implant diameter on primary implant stability, as well as their correlations were also evaluated.

METHODS

Dental implants with diameters of 3.75, 4, 5, and 6 mm and artificial bone specimens were scanned by microcomputed tomography to construct 3D models for calculating pBICA, BICA, and 3D BIC%. Indexes of the primary implant stability including the insertion torque value (ITV), Periotest value (PTV), and implant stability quotient (ISQ) were measured after implants with various diameters were placed into bone specimens. The Kruskal-Wallis test, Wilcoxon rank-sum test with Bonferroni adjustment, and Spearman correlations were all performed as statistical and correlation analyses.

RESULTS

The implant diameter significantly influenced pBICA and BICA, but not 3D BIC%. ITV and PTV were more sensitive to implant diameter than was ISQ. The coefficients of determination were high (>0.92) for the correlations between pBICA (or BICA) and indexes of the primary implant stability.

CONCLUSION

This study revealed how the implant diameter and the three-dimensional (3D) BIC influence the primary stabilities of dental implant. ITV and PTV were more sensitively influenced by the implant diameter than ISQ. The pBICA and BICA seem to be more important than 3D BIC % for using wider implant in treatment plan, since those two parameters are highly predictive of variations in the primary stability of dental implant.

[Primary radial head arthroplasty in trauma : Complications]

Radial head fractures are common injuries in elbow trauma. Non-displaced fractures are best treated conservatively. Simple but displaced fractures require anatomic reduction and fixation, typically using screws. The treatment course for complex fractures with multiple fragments is still being debated, as results are less predictable. Radial head resection is not advised if concomitant injuries of the coronoid process or the collateral ligaments with instability are present. Favorable outcomes following open reduction and fixation using plates were reported recently. However, complication rates are very high. Radial head replacement is a valuable tool in treating complex fractures of the radial head with predominantly good and excellent results. Patients who suffer radial head fractures are typically of a younger age, resulting in high functional demands. Certainly, unspecific and specific complications related to radial head arthroplasty were reported in up to 40 % of cases in an acute fracture setting. This article highlights common complications in radial head arthroplasty and aims to present strategies to avoid them.

Clinical and radiologic outcomes of pyrocarbon radial head prosthesis: midterm results

BACKGROUND

The modular pyrocarbon (MoPyC) radial head prosthesis (Tornier, Saint-Ismier, France) is a monoblock modular radial head prosthesis. This study assessed midterm outcomes after implantation of the prosthesis.

MATERIALS

A retrospective study was conducted of a consecutive cohort of 65 patients who underwent radial head replacement with the MoPyC prosthesis from January 2006 to April 2013. Indications were fractures, early or late failures from orthopedic or fixation treatments, and revisions after another implant. Patients were observed for >2 years for range of motion, pain, and stability; function by the Mayo Elbow Performance Score (total score, 100) and grip strength were assessed. Quality of stem implantation, bone resorption around the neck, and periprosthetic lucency were noted and quantified on radiographs. Capitellum shape and density as well as humeroulnar aspect (river delta sign) were evaluated. Complications and revision procedures were noted.

RESULTS

We evaluated 52 of 65 patients (mean follow-up, 46 ± 20 months; range, 24-108). The Mayo Elbow Performance Score was 96 ± 7; pain score, 42 ± 7/45; and motion score, 18 ± 2/20. Function and stability were excellent. Radiology revealed 92% of patients with cortical resorption around the neck without mechanical failure. Bone resorption was mostly anterior and lateral; it resolved within the first year and thereafter was stable. Eight patients underwent revision surgery for stiffness. No implant failures were noted.

CONCLUSION

Results of the MoPyC radial head prosthesis appear to be satisfactory. Bone resorption around the neck (stress shielding) is frequent and stable after 1 year and does not impair stem fixation. The MoPyC prosthesis appears to be a reliable solution for replacing the radial head.

Canal preparation for prosthetic radial head replacement: rasping versus reaming

BACKGROUND

While many design-specific features of radial head prostheses have been studied (ie, geometry and surface coating), the optimum technique for canal preparation has not been determined. We hypothesized that preparation of the radial canal with a reamer would allow for the accommodation of a larger stem diameter versus following canal preparation with a rasp, and would provide acceptable stem-bone micromotion.

METHODS

Paired proximal radii from 7 cadavers were prepared by a rasp on one side and a reamer on the contralateral side. Cementless radial head stems of increasing diameter were sequentially implanted up to the maximum size or until a fracture occurred and the micromotion between the stem and bone was recorded.

RESULTS

In 3 of 5 pairs, at least a 1 mm larger stem size fit into the canal after reaming versus after rasping (P = .04). 5 of 7 radii fractured secondary to intentional stem oversizing. For the optimally-sized stems, similar micromotion values were observed whether the canal was rasped (41 ± 6 μm) or reamed (44 ± 6 μm) (P = .72).

DISCUSSION

This study investigated an aspect of radial head arthroplasty technique about which little has currently been published. It is possible that use of a reamer rather than a rasp, while providing similar initial stability, might expand the stem size options for initial press-fit stability, and decrease the risk of fracture.

CONCLUSION

Radial canal preparation with a reamer allows for implantation of a 1 mm larger stem diameter versus rasping, while providing comparable initial stability to that achieved after rasping.

Prosthetic radial head stem pull-out as a mode of failure: a biomechanical study

PURPOSE

Press-fit cementless radial head implant longevity relies on adequate bone ingrowth. Failed implant osseointegration remains a clinical concern and has been shown to lead to prosthetic failure. The purpose of this study was to test the hypothesis that implants with sufficient initial press-fit stability would be less likely to fail due to implant pull-out, as demonstrated by an increasing amount of energy required to remove the prosthesis from the canal.

METHODS

Ten cadaveric radii were implanted with five sizes (6-10 mm in 1-mm increments) of grit-blasted, cementless radial head stems. A customised slap hammer was used to measure the energy required to remove each stem. Stem-bone micromotion was also measured.

RESULTS

The suboptimally sized stem (Max - 1) (i.e. 1 mm undersized) required less energy (0.5 ± 0 J) to pull out than the optimally sized stem (Max) (1.7 ± 0.3 J) (p = 0.008). The optimally sized stem demonstrated greater initial stability (45 ± 7 μm) than the suboptimally sized stem (79 ± 12 μm) (p = 0.004).

CONCLUSIONS

This investigation demonstrates the importance of obtaining adequate press-fit stability for the prevention of radial head stem pull-out failure. These data add to the relatively scant knowledge in the literature regarding radial head biomechanics. The energy required to remove a prosthetic radial head ingrowth stem decreases in conjunction with diameter. The use of an inadequately sized stem increases the stem's micromotion as well as the risk of prosthetic loosening due to pull-out.

Effect of stem length on prosthetic radial head micromotion

BACKGROUND

Osteointegration of press-fit radial head implants is achieved by limiting micromotion between the stem and bone. Aspects of stem design that contribute to the enhancement of initial stability (ie, stem diameter and surface coating) have been investigated. The importance of total prosthesis length and level of the neck cut has not been examined.

METHODS

Cadaveric radii were implanted with cementless, porous-coated radial head stems. We resected 10, 12, 15, 20, and 25 mm of radial neck in each specimen. Stem-bone micromotion was measured after each cut. Values were expressed in terms of quotients (cantilever quotient).

RESULTS

A threshold effect was observed at 15 mm of neck resection (cantilever quotient, 0.4), with a significant increase in micromotion observed between 12 mm (40 ± 10 μm) and 15 mm (80 ± 25 μm). A cantilever quotient of 0.35 or less predicted implant stability, whereas implants with a cantilever quotient of 0.6 or more were unstable. In between, the stems were "at risk" of instability.

CONCLUSION

Initial stem stability of a porous-coated, cementless radial head implant is dependent on length of the implant stem within bone and the level of the cut (amount of bone resected). Stability may be compromised by an implant with a combined head and neck length that is too long compared with the stem length within the canal. We found a critical ratio of exposed prosthesis to total implant length (cantilever quotient of 0.4), which puts the prosthesis at risk of inadequate initial stability. These data carry important implications for implant design and use.

Effects of rasp mismatch on plasma spray radial head stems

BACKGROUND

Radial head prosthetic stems designed for bone ingrowth are available with both plasma spray and grit blasted surfaces. A recent study comparing micromotion between the 2 demonstrated greater micromotion in the plasma spray than grit blasted stems, even though the latter had lower surface roughness. This raised the question that perhaps the size mismatch for grit-blasted radial head stems (0.5 mm) might be inadequate for plasma spray stems.

HYPOTHESIS

A tighter initial press-fit with plasma spray radial head stems may be gained by preparation with an undersized rasp.

METHODS

Paired cadaveric radii were implanted with plasma spray stems. The surgical control was prepared with a rasp designated for its corresponding stem size ("size-matched"), while the experimental group was prepared with a rasp 0.5 mm smaller than designated ("undersized").

RESULTS

The micromotion for the undersized rasp group (46 ± 12 μm) was not significantly different than for the size-matched rasp group (21 ± 12 μm) (P = .1).

DISCUSSION

Contrary to our hypothesis, no reduction in micromotion was observed when using an undersized rasp with a plasma spray stem. The micromotion results were not different from those observed when using a size-matched rasp, and actually approached significance in the opposite direction. This may be due to the rough stem surface chipping away bone fragments, rather than the bone being cut away precisely as is done with a rasp.

CONCLUSION

The use of an undersized rasp prior to implantation of a plasma spray radial head prosthesis does not confer any added benefit in terms of initial stability.

Effect of hoop stress fracture on micromotion of textured ingrowth stems for radial head replacement

BACKGROUND

Successful bone ingrowth around cementless implants requires adequate initial stability. Hoop stress fractures during stem insertion can potentially hinder prosthesis stability.

HYPOTHESIS

We hypothesized that an oversized radial head prosthetic stem (1 mm "too large" and causing a hoop stress fracture during insertion) would result in an unacceptable amount of micromotion.

MATERIALS AND METHODS

Grit-blasted radial head prosthetic stems were implanted into cadaveric radii. Rasp and stem insertion energies were measured, along with micromotion at the stem tip. The sizes were increased until a fracture developed in the radial neck.

RESULTS

Prosthetic radial head stems that were oversized by 1 mm caused small cracks in the radial neck. Micromotion of oversized stems (42 ± 7 μm) was within the threshold conducive for bone ingrowth (<100 μm) and not significantly different from that for the maximum sized stems (50 ± 12 μm) (P ≥ .4).

DISCUSSION

Contrary to our hypothesis, hoop stress fractures caused by implantation of a stem oversized by 1 mm did not result in loss of stability. Stem micromotion remained within the range for bone ingrowth and was not significantly diminished after the fracture. This suggests that if a crack occurs during the final stages of stem insertion, it may be acceptable to leave the stem in place without adding a cerclage wire.

CONCLUSION

A small radial neck fracture occurring during insertion of a radial head prosthetic stem oversized by 1 mm does not necessarily compromise initial stability.

Short- to mid-term results of metallic press-fit radial head arthroplasty in unstable injuries of the elbow

We assessed the short- to mid-term survival of metallic press-fit radial head prostheses in patients with radial head fractures and acute traumatic instability of the elbow.

The medical records of 42 patients (16 males, 26 females) with a mean age of 56 years (23 to 85) with acute unstable elbow injuries, including a fracture of the radial head requiring metallic replacement of the radial head, were reviewed retrospectively. Survival of the prosthesis was assessed from the radiographs of 37 patients after a mean follow-up of 50 months (12 to 107). The functional results of 31 patients were assessed using range-of-movement, Mayo elbow performance score (MEPS), Disabilities of the Arm, Shoulder and Hand (DASH) score and the RAND 36-item health survey.

At the most recent follow-up 25 prostheses were still well fixed, nine had been removed because of loosening, and three remained implanted but were loose. The mean time from implantation to loosening was 11 months (2 to 24). Radiolucent lines that developed around the prosthesis before removal were mild in three patients, moderate in one and severe in five. Range of movement parameters and mass grip strength were significantly lower in the affected elbow than in the unaffected side. The mean MEPS score was 86 (40 to 100) and the mean DASH score was 23 (0 to 81). According to RAND-36 scores, patients had more pain and lower physical function scores than normal population values.

Loosening of press-fit radial head prostheses is common, occurs early, often leads to severe osteolysis of the proximal radius, and commonly requires removal of the prosthesis.

Radial head replacement with unipolar and bipolar SBi system: a clinical and radiographic analysis after a 2-year mean follow-up

Radial head prosthetic replacement is indicated in case of comminuted fracture not amenable to internal fixation, especially when the radial head fracture is part of a pattern of lesions configuring a complex instability of the elbow. Thirty-one SBi radial head prostheses were implanted in 30 patients (one bilateral simultaneous fracture) over a 2 years period. In 10 patients, the mean time from trauma to surgical treatment was 2.4 days, while the remaining 20 patients were treated as "second opinion" cases presenting with elbow stiffness or instability after an average of 19 days from trauma. The implants were monopolar in 12 cases and bipolar in 19. The clinical results were evaluated through the Mayo Elbow performance scoring system. At an average follow-up of 2 years (range 13-36 months), the mean MEPS was 90 points (range 65-100). At late radiographic analysis, radiolucent lines around the stem were found in 11 of the 31 cases. Heterotopic ossifications were found in 14 cases. Bone resorption was observed in 9 cases. Two of the 31 prostheses were removed after 16 and 20 months, in one case to correct stiffness in pronation/supination, in the other one for asymptomatic aseptic mobilization. These short-term results are satisfactory, especially when considering that they were obtained in complex elbow lesions treated in many cases at a delayed stage. Our preference over time went more and more to bipolar implants, but from a comparison of the results we could find no evidence of a superiority of bipolar or monopolar implants. The evolution of these prostheses needs to be evaluated with further studies to assess mid-term and long-term follow-up results.

Alteration of the end-plane angle in press-fit cylindrical stem radial head prosthesis: an in vitro study

PURPOSE

Many studies comparing the morphology of native radial head with the prosthesis have been published. However, there is limited information regarding the postoperative alignment of the articular surface following the radial head replacement. The purpose of this study is to evaluate the alteration of the end-plane angle in the modular radial head prosthesis with a press-fit cementless cylindrical stem.

METHODS

The study used 36 cadaveric radii. The press-fit size prosthesis with cylindrical stem was inserted into each specimen. The end-plane angles of the radial head before and after prosthetic replacement, were measured in coronal and sagittal planes with a digital inclinometer. The data were analyzed by paired t-test.

RESULTS

From paired t-test, there were statistically symmetrical end-plane angles before and after radial head replacement in both coronal and sagittal planes (p-value < 0.01). The mean of radial head end-plane angle alteration in the coronal plane was 3.62° (SD, 2.76°) (range, 0.3°-8.9°). In the sagittal plane, the mean of alteration was 5.85° (SD, 3.56°) degrees (range, 0.3° - 14.2°).

CONCLUSION

The modular radial head prosthesis with cylindrical stem is in vitro able to restore the native end-plane angles of radial heads statistically when used in a press-fit fashion.

Forearm pain associated with loose radial head prostheses

BACKGROUND

After post-traumatic radial head replacement, pain caused by a loose prosthesis might incorrectly be assumed to be post-traumatic. Reliable guidelines for diagnosing a symptomatic loose radial head prosthesis are lacking. We noted that pain from a loose stem within the proximal radius may present as proximal radial forearm pain.

METHODS

The medical records and radiographs of 14 consecutive cases (13 patients) with proximal radial forearm pain associated with a loose radial head prosthesis were reviewed retrospectively. The indication for revision surgery was painful loosening of the prosthesis within the canal of the proximal radius in 7 patients (8 cases) and pain without preoperative confirmation of the loosening in 2 patients (2 cases). Various prosthetic designs had been used in the primary operations.

RESULTS

In 12 of 14 cases, the loosening was evident radiographically, but in 2 the only indication of a loose prosthesis (confirmed surgically) was proximal radial forearm pain. One patient was lost to follow-up. Revision or prosthetic removal eliminated the pain in 7 of 9 cases and decreased it in 1. One patient with moderate pain had an arthritic elbow and had no significant lasting relief from surgery. Follow-up averaged 27 months.

CONCLUSION

The presence of proximal radial forearm pain in a patient with a radial head prosthesis is an indicator of symptomatic mechanical loosening. If the prosthesis has a textured surface for bone ingrowth, and was inserted without cement, we now consider this a strong indicator of loosening, even in the absence of radiographic signs.

Micromotion of plasma spray versus grit-blasted radial head prosthetic stem surfaces

BACKGROUND

Initial stability of a textured surface prosthetic stem is necessary for bone in-growth. Surfaces currently used for radial head prostheses include titanium plasma spray and grit-blasted titanium.

HYPOTHESIS

Plasma spray radial head prosthetic stems are less dependent than grit-blasted stems on a tight press fit. Good initial press-fit stability, with acceptable micro-motion, can be achieved with a greater range of stem sizes using a plasma spray than grit-blasted surface.

METHODS

Paired cadaveric radii were implanted with plasma spray or grit-blasted radial head prosthetic stems. Micromotion at the stem tip was measured under circumstances simulating eccentric loads.

RESULTS

Micromotion in the plasma spray (PS) stems (49 ± 37) μm was not better than that in the grit-blasted (GB) stems (28 ± 10) μm (P = .13). Micromotion of less than 100 μm was measured in all 12 GB stems that were maximum or 1 mm less than maximum size, versus 5/6, and 4/6 PS stems, respectively.

DISCUSSION

Micromotion in plasma spray prosthetic radial head stems was not better than that seen in grit-blasted stems, contrary to our initial hypothesis.

CONCLUSION

Grit-blasted prosthetic radial head stems confer initial press-fit stability that is as good as, or slightly better than, corresponding plasma spray stems. Acceptable amounts of micromotion can be achieved with 2 grit-blasted stem sizes and probably with 2 plasma spray stem sizes.

Radial head prosthesis micromotion characteristics: Partial versus fully grit-blasted stems

BACKGROUND

Compared to fully textured prosthetic stems, partial texturing lessens bone loss due to stress shielding and makes removal easier. However, initial press-fit stability is necessary for bone ingrowth.

HYPOTHESIS

There is no significant difference in the initial stability of radial head prostheses that are partially grit-blasted compared to those that are fully grit-blasted.

MATERIALS AND METHODS

Cadaveric radii were implanted with partial or fully grit-blasted radial head prostheses. Micromotion of the stem at the isthmus of the canal and stem tip were measured under circumstances simulating eccentric loads.

RESULTS

Micromotion was not significantly different in the fully grit-blasted stems (isthmus, 11 ± 1 μm; tip, 21 ± 2 μm) and partially grit-blasted stems (isthmus, 13 ± 2 μm; tip, 25 ± 2 μm) (P = 0.4). The direction of loading had no effect on micromotion characteristics in either the fully or partially grit-blasted stems (P = .07).

DISCUSSION

Micromotion is comparable in partially and fully grit-blasted radial head prosthetic stems. For both stem surfaces, micromotion was well within the range that is conducive for bone ingrowth. A partially textured stem might have less bone loss due to stress shielding, making it easier to remove without destroying bone.

CONCLUSION

The initial stability of a radial head stem that is partially grit-blasted only at the proximal end is comparable to that of a radial head stem that is grit-blasted along its entire length.