The geometry of the humeral head and the design of prostheses

Does forearm referencing using a retroversion guide achieve the targeted retroversion of the humeral component in reverse shoulder arthroplasty?

BACKGROUND

Component positioning affects clinical outcomes of reverse shoulder arthroplasty, which necessitates an implantation technique that is reproducible, consistent, and reliable. This study aims to assess the accuracy and precision of positioning the humeral component in planned retroversion using a forearm referencing guide.

METHODS

Computed tomography scans of 54 patients (27 males and 27 females) who underwent primary reverse shoulder arthroplasty for osteoarthritis or cuff tear arthropathy were evaluated. A standardized surgical technique was used to place the humeral stem in 15° of retroversion. Version was assessed intraoperatively visualizing the retroversion guide from above and referencing the forearm axis. Metal subtraction techniques from postoperative computed tomography images allowed for the generation of 3D models of the humerus and for evaluation of the humeral component position. Anatomical humeral plane and implant planes were defined and the retroversion 3D angle between identified planes was recorded for each patient. Accuracy and precision were assessed. A subgroup analysis evaluated differences between male and female patients.

RESULTS

The humeral retroversion angle ranged from 0.9° to 22.8°. The majority (81%) of the measurements were less than 15°. Mean retroversion angle (±SD) was 9.9° ± 5.8° (95% CI 8.4°-11.5°) with a mean percent error with respect to 15° of -34% ± 38 (95% CI -23 to -44). In the male subgroup (n = 27, range 3.8°-22.5°), the mean retroversion angle was 11.9° ± 5.4° (95% CI 9.8°-14.1°) with a mean percent error with respect to 15° of -21% ± 36 (95% CI -6 to -35). In the female subgroup (n = 27, range 0.9°-22.8°), mean retroversion angle was 8.0° ± 5.5° (95% CI 5.8°-10.1°) and the mean percent error with respect to 15° was -47% ± 36 (95% CI -32 to -61). The differences between the 2 gender groups were statistically significant (P = .006).

CONCLUSION

Referencing the forearm using an extramedullary forearm referencing system to position the humeral stem in a desired retroversion is neither accurate nor precise. There is a nonnegligible tendency to achieve a lower retroversion than planned, and the error is more marked in females.

3D-Analysis of the Proximal Humeral Anatomy Before and After Stemless Shoulder Arthroplasty-A Prospective Case Series Study

BACKGROUND

Stemless shoulder arthroplasty (SSA) is used to anatomically reconstruct proximal humerus geometry and preserve proximal humerus bone stock. The current literature lacks 3D-analysis of pre- and postoperative proximal humeral anatomy after SSA. The aim of this study was to prospectively analyze the humeral head anatomy using a computer-assisted topography mapping technique after SSA in relation to the preoperative status and the contralateral (not affected) side.

METHODS

Twenty-nine patients (mean age: 63.5 ± 11.7 years) affected by primary shoulder osteoarthritis and treated with SSA were included. Preoperative and postoperative CT scans of the affected and contralateral sites were analyzed regarding joint geometry. Clinical outcome was assessed by Constant and Disabilities of the Arm, Shoulder and Hand (DASH) score shortly before and one year after surgery.

RESULTS

Clinical outcome improved significantly. No correlation between clinical outcome and the evaluated anatomical parameters was found. There was a significant decrease of the humeral head height (p < 0.01) and radius (p = 0.03) in the preoperative versus the postoperative joint geometry. The comparison to the contralateral site showed also a significant decrease of the humeral head height (p < 0.01). All other parameters showed no significant differences.

CONCLUSION

Proximal humeral anatomy can be almost anatomically reconstructed by SSA. Solely the humeral head height differs significantly to the preoperative as well as contralateral morphology.

Do Modern Designs of Metal-Backed Glenoid Components Show Improved Clinical Results in Total Shoulder Arthroplasty? A Systematic Review of the Literature

Background:

Despite the increased popularity of reverse total shoulder arthroplasty, total shoulder arthroplasty is the standard treatment for advanced shoulder arthritis in young adult patients. Conventional metal-backed glenoid (MBG) designs result in more loosening and revision surgery compared with cemented polyethylene glenoid components. However, modern MBG designs have been recently devised to overcome such drawbacks.

Purpose:

To compare the radiolucency, loosening, and failure rates of modern MBG designs with those of conventional designs.

Study Design:

Systematic review; Level of evidence, 4.

Methods:

A search for relevant articles was carried out using the PubMed, Cochrane Library, and Embase databases using MeSH (Medical Subject Headings) terms and natural keywords. A total of 362 articles were screened. We descriptively analyzed numerical data between the groups and statistically analyzed categorical data, such as the presence of loosening, failure, and revision surgery. The main outcome was the rate of revision surgery or failure. Subgroup analysis according to follow-up duration was performed to reduce heterogeneity.

Results:

A total of 25 articles (2036 shoulders) were included; 15 articles (1579 shoulders) involved a conventional MBG design, and 10 (457 shoulders) involved a modern design. The mean age of the patients was 64.2 and 66.5 years in the conventional and modern design groups, respectively, with a mean follow-up duration of 102.0 and 56.1 months, a mean gain of forward elevation of 35.1° and 61.7°, and a mean gain of external rotation of 24.2° and 39.2°. The rate of radiolucency was 48.0% and 16.7%, the rate of loosening was 11.2% and 4.9%, and the rate of revision was 15.9% and 2.4%, for the conventional and modern design groups, respectively. Subgroup analysis according to follow-up duration showed that the rates of loosening and revision were significantly lower in the modern design group (P < .001).

Conclusion:

Our findings suggest that modern MBG designs showed significantly lower loosening and failure rates than conventional designs. The overall results of the comparison, including loosening, failure, change in range of motion, and clinical scores, indicate that modern MBG designs are promising. More long-term follow-up studies on modern MBGs should be conducted.

An interpopulation comparison of 3-dimensional morphometric measurements of the proximal humerus

Background

Precise anatomic reconstruction of the proximal humerus is essential to a favorable outcome of total shoulder arthroplasty. Because of the wide variation in the geometric features of the proximal humerus, prosthetic designs incorporating these disparities are being developed.

Methods

The aim of this study is to use data obtained from cadavers and computed tomographic scans to investigate the 3-dimensional morphometric parameters of the proximal humerus of South African and Swiss samples and make an interpopulation comparison. In addition, the study combines the interarticular variations between populations with the differences in sex and shoulder sides. With the aid of medical imaging techniques and engineering design tools, various geometric features were measured.

Results

The results obtained from these analyses revealed several differences in sex and shoulder sides. On average, the Swiss were larger in most of the measured parameters than the South Africans. The male shoulders of Swiss and South Africans were observed to significantly vary in 4 of the parameters measured. The South African male and female right shoulders varied considerably in one-fourth of the measured shoulder variables. Generally, for both populations, the left and right shoulders of the same individuals were not different in all the measured variables irrespective of sex.

Conclusion

The knowledge acquired in this study is expected to assist in the development of a population-specific shoulder prosthetic design and surgical planning procedures.

The Walch type B humerus: glenoid retroversion is associated with torsional differences in the humerus

BACKGROUND

The Walch type B glenoid has the hallmark features of retroversion, joint subluxation, and bony erosion. Although the type B glenoid has been well described, the morphology of the corresponding type B humerus is poorly understood. As such, the aim of this imaging-based anthropometric study was to investigate humeral torsion in Walch type B shoulders.

METHODS

Three-dimensional models of the full-length humerus were generated from computed tomography data for the Walch type B group (n = 59) and for a control group of normal nonarthritic shoulders (n = 59). An anatomic humeral head-neck plane was created and used to determine humeral torsion relative to the epicondylar axis. Measurements were repeated, and intraclass correlation coefficients were calculated.

RESULTS

The type B humeri had significantly (P < .001) less retrotorsion (14° ± 9°) than the control group (36° ± 12°) relative to the epicondylar axis. Male and female individuals within the control group showed statistically significant differences in humeral torsion (P = .043), which were not found in the type B group. Inter-rater reliability showed excellent agreement for humeral torsion (intraclass correlation coefficient, 0.962). A subgroup analysis between Walch type B2 and B3 shoulders showed no significant differences in any of the humeral or glenoid parameters.

CONCLUSION

The Walch type B humerus has significantly less retrotorsion than non-osteoarthritic shoulders. At present, it is unknown whether the altered humeral retrotorsion is a cause or effect of the type B glenoid. In addition, it is unknown whether surgeons should be reconstructing type B2 humeral component version to pathologic torsion or to nonpathologic population means to optimize arthroplasty survivorship.

The Circle-Fit Method Helps Make Reliable Cortical Thickness Measurements Regardless of Humeral Length

Background

Although proximal humerus strength/quality can be assessed using cortical thickness measurements (eg, cortical index), there is no agreement where to make them. Tingart and coworkers used measurements where the proximal endosteum becomes parallel, while Mather and coworkers used measurements where the periosteum becomes parallel. The new circle-fit method (CFM) makes 2 metaphyseal (M1-M2) and 6 diaphyseal (D1-D6) measurements referenced from humeral head diameter (HHD). However, it is unknown whether these locations correlate to humeral length (HL). Accordingly, we asked: (1) Does HHD, Tingart distance, and Mather distance correlate with HL? (2) What is the location of HHD, Tingart distance, and Mather distance as a percentage of HL? and (3) Which CFM D1-D6 locations correlate with Tingart and Mather distances?

Materials and Methods

Measurements made on cortical thickness (CT) scout views of 19 humeri (ages: 16-73 years) included HHD, distances from the superior aspect of the humerus to proximal Tingart and Mather locations, and HL.

Results

Intraclass correlation was excellent for CFM-HHD, poor for Tingart, and moderate for Mather. The CFM-HHD had a stronger correlation to HL than Tingart and Mather. Mean HHD was 15.5% (0.9%) of HL while Tingart was 27.0% (4.1%) and Mather was 23.2% (3.8%). Tingart distance corresponded to D2/D3 CFM locations while the Mather distance was similar to D1/D2.

Discussion

The CFM reliably correlates with HL and provides a stronger correlation and less variance between specimens than the Tingart or Mather Methods.

Conclusions

Because the CFM produces reliable percent of HL locations, it should be used to define locations for obtaining biomechanically relevant CT measurements such as cortical index. Stronger correlations of these CFM-based measurements with proximal humerus strength will be important for developing advanced algorithms for fracture treatment.

Is global humeral head offset related to intramedullary canal width? A computer tomography morphometric study

Background

While most anatomic TSA stems allow some intra-operative adjustments, the default configuration assumes that head offset is directly proportional to stem diameter. Some authors reported that humeral head diameter is proportional to intra-medullary canal width and humeral head offset, but none investigated the direct relationship between head offset and endosteal measurements. The purpose of the study was to determine whether global humeral head offset is proportional to intramedullary canal width at the distal metaphysis and proximal diaphysis.

Methods

We analyzed 100 Computed Tomography shoulder scans of patients aged 59.1 ± 20.5 with no signs of gleno-humeral arthritis nor humeral dysplasia. The width of the intramedullary diaphyseal canal was determined at four transverse sections 65, 70, 100 and 105 mm below the head center. The inter-observer agreement was excellent for intramedullary canal width (ICC = 0.96), head diameter (ICC = 0.97) and global head offset (ICC = 0.85). Correlations were analysed using Pearson’s coefficients and multivariable regressions were performed to determine associations between head offset and five independent variables (gender, age, intramedullary canal width, head diameter).

Results

Global head offset was negatively correlated with head diameter (r = − 0.31, p = 0.002), but not correlated with intramedullary canal width (r = − 0.11, p = 0.282). Multivariable regression confirmed that global head offset was independently associated with head diameter (beta = − 0.15, p = 0.005), but not with intramedullary canal width (beta = 0.06, p = 0.431).

Conclusions

The present study revealed that humeral offset is not correlated with intramedullary canal width. Implant manufacturers and shoulder surgeons should be aware of the subtle morphologic features, to enhance humeral stem design and restore native anatomy.

A 3D comparison of humeral head retroversion by sex and measurement technique

BACKGROUND

Accurate humeral head reconstruction during shoulder arthroplasty is partially dependent on correctly estimating and replicating native version. The present study evaluated the effects of sex and measurement technique on three-dimensional (3D) humeral version measurements made using the transepicondylar, forearm and flexion-extension axes.

METHODS

Fifty-two full-arm computed tomography scans were converted to 3D models and geometry extracted to define landmarks and coordinate systems. An anatomic humeral head osteotomy plane was used to measure version relative to the three measurement techniques and compare between sexes.

RESULTS

The measurement technique used had a significant affect (p < 0.001) on the resulting version measurement. The forearm axis technique consistently resulted in higher measured version compared to either the flexion-extension [mean (SD) males 9° (4°), females 13° (5°), p < 0.001] or the transepicondylar axes [mean (SD) males 8° (4°), females 11° (4°), p < 0.001]. Version in males was 7° greater than females when referencing either the flexion-extension [p = 0.029; mean (SD) males 37.7° (11°), females 30.4° (13°)] or transepicondylar axes [p = 0.045; mean (SD) males 39° (11°), females 32° (12°)].

CONCLUSIONS

The choice of measurement technique can affect the humeral version angle. These results are important because measuring version using the epicondyles pre-operatively, and subsequently the forearm intra-operatively, will result in approximately 10° under-retroverted osteotomy. For example, 0° neutral version cut during reverse arthroplasty measured referencing the forearm results in 10° anteverted osteotomy when referencing the distal humerus.

Spherical versus elliptical prosthetic humeral heads: a comparison of anatomic fit

BACKGROUND

The aim of this study was to quantify the influence of prosthetic humeral head shape, as well as the number of available prosthetic head sizes, on replicating the normal humeral head anatomy during shoulder reconstructive surgery.

METHODS

Computer modeling software was used to create virtual sets of both spherical and elliptical prosthetic heads, which were virtually implanted into 3-dimensional computed tomography scan-based models of 79 proximal humeri. Anatomic replication was considered successful if the measured parameters (diameters of the base of the head in the frontal and sagittal planes, radii of curvature in the frontal and sagittal planes, and humeral head height) were all reproduced within 3 mm. The Fisher exact test was used to compare the percentage of successful replications for both head types and to compare differences resulting from the use of sets with fewer or more available head sizes. Statistical significance was set at P ≤ .05.

RESULTS

Regardless of the number of available head sizes per set, it was possible to replicate the normal anatomy within 3 mm in a higher percentage of specimens using elliptical (96%-100%) as opposed to spherical (41%-78%) prosthetic heads (P ≤ .0013).

CONCLUSION

Compared with use of spherical prosthetic heads, use of elliptical heads resulted in improved replication of the normal humeral head shape. In light of the emerging evidence that use of anatomically shaped prosthetic humeral heads might lead to better shoulder function and possibly improved implant survivorship, the findings of this study may have important clinical and economic implications.

Does prosthetic humeral articular surface positioning associate with outcome after total shoulder arthroplasty?

BACKGROUND

The purpose of this study was to determine the effect of humeral articular component positioning on changes in patient-reported outcomes after anatomic total shoulder arthroplasty.

METHODS

This was a retrospective series of consecutive patients at 2 high-volume referral centers. The study included patients with (1) a preoperative and postoperative radiograph demonstrating a perfect or nearly perfect profile of the humerus and implant and (2) Simple Shoulder Test, visual analog scale for pain, and American Society of Shoulder and Elbow Surgeons (ASES) Standardized Shoulder Assessment scores preoperatively and at greater than 2 years postoperatively. Head height, head diameter, tuberosity-to-head height distance, inclination, and medial offset of the center of rotation (COR) were measured preoperatively and postoperatively. Distance and direction from the ideal COR to the reconstructed center of rotation was measured. Measurements were correlated with improvement in functional outcomes.

RESULTS

The study included 95 patients, aged 66 ± 9 years, with a mean follow-up of 4.3 ± 1.7 years. An a priori power analysis suggested that a sample size of 95 patients provided 80% power to detect correlations of R² = 0.07. The COR shift was >2 mm in 62% of patients and >4 mm 15%. Thirty-two percent had a change of ASES of <21 points. On multivariate analysis, there were no significant associations between any change in measured prosthetic radiographic parameters and changes in the visual analog scale, Simple Shoulder Test, or ASES scores (P > .05).

CONCLUSION

In this retrospective analysis of total shoulder arthroplasty in which most components were well positioned, humeral component positioning did not associate with change in postoperative outcomes. These findings should be prospectively confirmed.

An analysis of proximal humerus morphology with special interest in stemless shoulder arthroplasty

BACKGROUND

Shoulder arthroplasty evolution has resulted in the shortening of traditional stemmed humeral components. Newer stemless implants rely on structures that maintain fixation in the metaphyseal region of the proximal humerus. Whereas the overall morphology of the proximal humerus is well understood, the advent of stemless implants requires that additional geometric measures be assessed. This study's purpose was to introduce new anatomic measures to assist with the design of stemless implants.

METHODS

Using computed tomography data from 98 subjects (nonarthritic [n = 41], B2 osteoarthritic [n = 26], and symmetric osteoarthritic [n = 31]), shifts in proximal canal direction, bounding diameters along the canal, and canal depth beneath the center of the humeral resection plane were quantified. Traditional articular aspect ratio terms (ie, resection diameter, humeral head height) were also quantified. All measures were reported relative to a humeral coordinate system relevant to stemless implants.

RESULTS

Humeral depth, gender, and osteoarthritis were found to have effects on the measured parameters. Of these factors, gender was the most prominent, as men presented with significantly larger canal diameters and depths than women did (P < .001). Osteoarthritis had less of a significant impact on results (P < .001), with the attributed differences in canal path direction and articular aspect ratio being small in absolute value. Canal diameter was found to change significantly as a function of depth beneath the resection plane (P < .001).

CONCLUSIONS

This work quantified 3 new morphologic terms relevant to proximal humerus stemless arthroplasty. Together, these outcome measures help define the spatial limits for stemless humeral arthroplasty in an implant-relevant coordinate system.

An assessment of proximal humerus density with reference to stemless implants

BACKGROUND

Shoulder arthroplasty humeral components have undergone several generational changes, with systems now offering shorter stems and stemless options. The stemless humeral implants obtain fixation in the trabecular bone of the proximal humerus through elaborate fixation features. To optimize implant design, the regional variations in bone density within the proximal humerus should be determined. As such, the purpose of this computed tomography-based study was to map the regional variations in bone density of the proximal humerus.

METHODS

The trabecular-canal of the proximal humerus was extracted from computed tomography scans of 98 subjects and divided into 13 slices and 5 subsections (central, anterior, posterior, medial, and lateral). The average apparent density (ρ_AVG) was then quantified in each subsection of the trabecular-canal.

RESULTS

Slice depth, subsection, and gender were all significant main effects, with additional significant interactions between slice depth, subsection, and osteoarthritic condition. The slices above the resection plane had the greatest ρ_AVG, with densities decreasing down the canal. The central subsection had significantly lower ρ_AVG than the peripheral sections, and the medial subsection tended to have the highest ρ_AVG (P < .001). Furthermore, the ρ_AVG of male subjects was significantly greater than that of female subjects (P < .001).

CONCLUSIONS

The apparent density of the proximal humerus' trabecular-canal is nonuniform. This has implications for the design of stemless implants, indicating that implants seeking purchase in higher density bone should take advantage of the peripheral regions of the trabecular-canal within the first 15-20 mm beneath the humeral head resection plane.

Humeral head circle-fit method greatly increases reliability and accuracy when measuring anterior-posterior radiographs of the proximal humerus

Measurements made on routine A-P radiographs can predict strength/quality of the proximal humerus, as shown in terms of two easy-to-measure parameters: Cortical index (CI) and mean-combined cortical thickness (MCCT). Because of high variability inherent when using established methods to measure these parameters, we describe a new orientation system. Using digitized radiographs of 33 adult proximal humeri, five observers measured anatomical reference locations in accordance with: (i) Tingart et al. (2003) method, (ii) Mather et al. (2013) method, and (iii) our new humeral head Circle-Fit method (CFM). The Tingart and Mather methods measure CI and MCCT with respect to upper and lower edges of 20 mm tall rectangles fit to a proximal diaphyseal location where endosteal (Tingart) or periosteal (Mather) cortical margins become parallel. But high intra- and inter-observer variability occurs when placing the rectangles because of uncertainty in identifying cortical parallelism. With the CFM an adjustable circle is fit to the humeral head articular surface, which reliably and easily establishes a proximal metaphyseal landmark (M1) at the surgical neck. Distal locations are then designated at successive 10 mm increments below M1, including a second metaphyseal landmark (M2) followed by diaphyseal (D) locations (D1, D2 ⋯D6). D1 corresponds most closely to the proximal edges of the rectangles used in the other methods. Results showed minimal inter-observer variations (mean error, 1.5 ± 1.1 mm) when the CFM is used to establish diaphyseal locations for making CI and MCCT measurements when compared to each of the other methods (mean error range, 10.7 ± 5.9 to 13.3 ± 6.7 mm) (p < 0.001). © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2313-2322, 2017.

Outcome and revision rate of uncemented glenohumeral resurfacing (C.A.P.) after 5-8 years

BACKGROUND

Resurfacing of the glenohumeral joint for patients with glenohumeral arthritis has gained popularity since the first introduction. We report the mid-term results of the Global C.A.P. uncemented resurfacing shoulder prosthesis (DePuy Synthes).

METHODS

From January 2007 to December 2009, 48 humeral cementless resurfacing prostheses in 46 patients were performed. All patients were diagnosed with primary glenohumeral osteoarthritis. Patients were contacted for review; the Constant Score, visual analog pain scale, Dutch Simple Shoulder Test, SF-12 scores and physical examination were assessed both preoperatively and yearly postoperatively. Complications and revision surgery were documented. Radiographs were evaluated for component size, offset, inclination, height, loosening and subluxation.

RESULTS

Forty-six patients (12 males) with a mean age of 72 years old (range 59-89) were included. At a mean 6.4-year follow-up (range 5-8), the Constant Score, visual analog pain scale and the Dutch Simple Shoulder Test scores improved significantly (p < 0.05) from baseline. Three patients were lost to follow-up. One patient died and two patients were not able to attend the follow-up appointments, due to other health-related issues. Eleven patients (23%) had a revision operation.

CONCLUSIONS

The most important findings of this study of the Global C.A.P. shoulder resurfacing arthroplasty were an increase of range of motion, a reduction of pain complaints, but a concerning high rate of revision after mid-term follow-up.

LEVEL OF EVIDENCE

Therapeutic Level IV.

Distinct Proximal Humeral Geometry in Chinese Population and Clinical Relevance

BACKGROUND

Replicating humeral anatomy during shoulder arthroplasty is important for good patient outcomes. The proximal humeral geometry of the Chinese population has been rarely reported. We analyzed the geometry of the proximal part of the humerus in Chinese subjects and compared it with that of Western populations and the dimensions of available prostheses.

METHODS

Eighty healthy Chinese subjects underwent computed tomography (CT)-arthrography. Three-dimensional (3D) digital humeral and glenoid models were reconstructed, and geometric parameters were measured. Humeral measurements included the radius of curvature, articular surface diameter and thickness, anterior-posterior/superior-inferior (AP/SI) articular surface diameter ratio, articular surface thickness/radius of curvature ratio, surface arc, inclination angle, retroversion angle, and medial and posterior offsets. Glenoid measurements included SI length, AP length, SI radius, and AP radius.

RESULTS

The average radius of curvature (and standard deviation) of the humeral head was 22.1 ± 1.9 mm, the articular surface diameter averaged 42.9 ± 3.6 mm, and the articular surface thickness averaged 16.9 ± 1.5 mm. There was strong linear correlation between the articular surface diameter and thickness (r = 0.696, p = 0.001), with a linear regression relationship of thickness = 0.357 × diameter + 1.615. The AP/SI articular surface diameter ratio averaged 0.93 ± 0.03; the articular surface thickness/radius of curvature ratio, 0.77 ± 0.05; the surface arc, 153° ± 5.6°; the inclination angle, 133° ± 3.1°; and the retroversion angle, 22.6° ± 10.2°. The medial and posterior offsets averaged 6.3 ± 0.9 mm and 0.4 ± 0.78 mm, respectively; the SI and AP lengths, 30.15 ± 3.70 mm and 20.35 ± 2.56 mm; and the SI and AP radii, 23.49 ± 2.48 mm and 25.54 ± 3.07 mm. Compared with the Western population, the Chinese cohort had a smaller radius of curvature (p < 0.001), smaller articular surface diameter (p = 0.009), larger articular surface thickness/radius of curvature ratio (p < 0.001), larger surface arc (p < 0.001), smaller inclination angle (p < 0.001), and smaller posterior offset (p < 0.001). Unlike the Western population, the Chinese population had higher glenohumeral conformity in the coronal plane than in the axial plane. Many manufacturers' shoulder prostheses do not adequately cover the range of humeral head dimensions in our Chinese cohort.

CONCLUSIONS

The geometric parameters of the humeri in the Chinese population differ from those in other populations. These differences have clinical relevance with regard to implant design and arthroplasty technique and likely affect clinical outcomes.

Association of lateral humeral offset with functional outcome and geometric restoration in stemless total shoulder arthroplasty

BACKGROUND

Restoration of shoulder geometry is desirable in total shoulder arthroplasty (TSA) and thought to influence the postoperative clinical outcome. We aimed to study the association of postoperative lateral humeral offset (LHO) changes and clinical outcome, as well as to investigate the ability of stemless anatomic TSA to restore shoulder geometry.

METHODS

In patients with primary shoulder osteoarthritis who underwent stemless anatomic TSA, the preoperative and postoperative clinical outcome was measured. Shoulder geometry was measured on preoperative computed tomography for the osteoarthritic shoulder and contralateral healthy shoulder and on postoperative computed tomography for the operated shoulder.

RESULTS

Forty-four patients with a minimum follow-up of 12 months (range, 12-50 months) were available for the study. Postoperatively, the clinical outcome measures improved. The postoperative difference in LHO between the operated shoulder and contralateral healthy shoulder was 1.3 ± 4.6 mm and was correlated with scores on the short version of the Disabilities of the Arm, Shoulder and Hand questionnaire at 3 months (Pearson correlation = 0.36, P = .01) and visual analog scale for pain at rest (Pearson correlation = 0.30, P = .03) and with exertion (Pearson correlation = 0.34, P = .01) at 3 months. Lengthening of LHO was associated with worsening shoulder function at 3 months but not at 12 months. The postoperative shoulder geometric parameters were restored postoperatively to acceptable ranges.

CONCLUSION

The stemless anatomic TSA could restore shoulder geometry in an acceptable manner. At 3 months but not at 12 months, increased LHO had a negative effect on shoulder function and resulted in more shoulder pain at rest and with exertion but did not affect quality of life, health status, or range of motion.

An anthropometric analysis to derive formulae for calculating the dimensions of anatomically shaped humeral heads

BACKGROUND

The elliptical shape of the humeral head has been vaguely described, but a more detailed mathematical description is lacking. The primary goal of this study was to create formulae to describe the mathematical relationships between the various dimensions of anatomically shaped humeral heads.

METHODS

Three-dimensional computer models of 79 proximal humeri derived from computed tomography scans (white subjects, 47 male and 32 female; ages, 17-87 years) were studied. Linear regression analysis of the obtained humeral measurements was performed, and Pearson correlation coefficient (R) values were calculated. To substantiate the results of the linear regression analysis, Welch t-test was used to compare various parameters of small, medium, and large humeral heads.

RESULTS

Formulae for calculating humeral head height, diameters of the base of the humeral head in the frontal and sagittal planes, and radii of curvature in the frontal and sagittal planes were derived from the linear regression plots that were found to have strong (1 ≥ R ≥ 0.50) correlations. By Welch t-test, differences between the 3 head sizes were statistically significant in each case (P ≤ .022). The elliptical shape of the base of the humeral head was found to elongate with increasing humeral head size.

CONCLUSIONS

Mathematical formulae relating various humeral head dimensional measurements are presented. The formulae derived in this study may be useful for the design of future prosthetic shoulder systems in which the goal is to replicate normal anatomy. This is the first study to describe that the elliptical shape of the base of the humeral head elongates as head size increases.

Three-dimensional anthropometric analysis of the glenohumeral joint in a normal Japanese population

BACKGROUND

An understanding of normal glenohumeral geometry is important for anatomical reconstruction in shoulder arthroplasty. Unfortunately, the details of the glenohumeral joint in Asian populations have not been sufficiently evaluated. The purpose of this study was to evaluate the 3-dimensional geometry of the glenohumeral joint in the normal Japanese population and to clarify its morphologic features.

METHODS

Anthropometric analysis of the glenohumeral joint was performed using computed tomography scans of 160 normal shoulders from healthy Japanese volunteers. The glenohumeral dimensions and orientation were analyzed 3-dimensionally. Sex differences and correlations between sides and among the respective parameters in the glenohumeral dimensions were evaluated.

RESULTS

The normal Japanese humeral head has an average width of 41.4 mm, thickness of 13.2 mm, diameter of 42.9 mm, retroversion of 32°, and inclination of 135°. The glenoid has an average height of 31.5 mm, width of 23.1 mm, diameter of 62.0 mm, retroversion of 0°, and inferior inclination of 2°. The values of the glenohumeral dimensions were uniform in men and women, and the humeral head and glenoid were larger in men than in women. The glenohumeral size was well correlated between the 2 sides, and there were direct correlations among the heights, humeral length, humeral head size, and glenoid size.

CONCLUSIONS

The present study revealed the glenohumeral geometry in the normal Japanese population. The present results would be useful to determine the size of implants and to improve the design of shoulder prostheses that reflect the normal anatomy of the Asian glenohumeral joint.

Optimizing intramedullary entry location on the proximal humerus based on variations of neck-shaft angle

BACKGROUND

The purpose of this study was to define the relationship between the humeral neck-shaft angle (NSA) and variations in the ideal entry portal aligned with the long axis of the intramedullary canal of the proximal humerus.

METHODS

Three-dimensional images of 36 cadaveric humeri with various NSAs were reconstructed by a computerized surgical simulation program. The anteroposterior, mediolateral, and linear distances between a line from the center of the proximal medullary canal to the bicipital groove were measured. Differences among humeri with various NSAs were analyzed.

RESULTS

The intramedullary axis line was located a mean of 9 ± 2 mm posteriorly and 11 ± 3 mm medially from the bicipital groove. The axis line was 9 ± 2 mm posterior and 11 ± 2 mm medial with a standard NSA. The axis line in humeri with a varus NSA was 8 ± 2 mm posteriorly and 9 ± 2 mm medially, whereas the axis line was 10 ± 3 mm posteriorly and 14 ± 3 mm medially with a valgus NSA. The differences in the mediolateral distances between the groups were significant (P < .00009).

CONCLUSION

Care should be taken in choosing the entry portal position in humeri with various NSAs as the entry portal position differs according to the NSA. It is recommended that the location of the entry portal be moved toward the center of the humeral head to align with the centerline of the intramedullary canal in humeri with a valgus NSA in particular.

Radiostereographic analysis of a shoulder surface replacement: does hydroxyapatite have a place?

Resurfacing of the humeral head is commonly used within the UK to treat osteoarthritis (OA) of the shoulder. We present the results of a small prospective randomised study of this procedure using the Global CAP prosthesis with two different coatings, Porocoat and DuoFix hydroxyapatite (HA). We followed two groups of ten patients with OA of the shoulder for two years after insertion of the prosthesis with tantalum marker beads, recording pain, Constant-Murley and American Shoulder and Elbow Surgeons (ASES) outcome scores, and using radiostereometric analysis to assess migration. The outcomes were similar to those of other series, with significant reductions in pain (p = 0.003) and an improvement in the Constant (p = 0.001) and ASES scores (p = 0.006). The mean migration of the prosthesis three months post-operatively was 0.78 mm (0.51 to 1.69) and 0.72 mm (0.33 to 1.45) for the Porocoat and DuoFix groups, respectively. Analysis of variance indicated that the rate of migration reached a plateau after three months post-operatively in both groups. At follow-up of two years the mean migration was 1 mm (sd 1 (0.25 to 3.32)); in the Porocoat group and 0.8 mm (sd 0.4 (0.27 to 1.45)) in the DuoFix HA group. Significant migration of the prosthesis was seen in one patient who had received an anterior humeral bone graft. This prosthesis was later revised after 2.7 years. The addition of a coating of HA to the sintered surface does not improve fixation of this prosthesis.

Short-term results of the global C.A.P. uncemented resurfacing shoulder prosthesis

The authors report the 2-year results of an uncemented resurfacing shoulder prosthesis in 47 patients with primary glenohumeral osteoarthritis who underwent a cementless humeral resurfacing arthroplasty between 2007 and 2009. Constant scores (corrected for sex and age), shoulder function, visual analog pain scales, Dutch Simple Shoulder Tests, and physical SF-12 scores improved significantly (P<.05) from preoperatively to 2 years postoperatively. Mental SF-12 scores remained the same. Complications included 1 traumatic lesser tuberosity avulsion fracture, 1 intra-articular loose body due to a fractured osteophyte, and 1 subscapularis tendon rupture. No patient required revision surgery for any reason. Cementless humeral resurfacing arthroplasty is a viable treatment option for primary glenohumeral arthritis.

Review of bicipital groove morphology and its analysis in north Indian population

The variant morphometry of bicipital groove is reported to be associated with pathologies of biceps tendon and is useful in surgical procedures in this region. The pathologies of biceps tendon are frequent causes of shoulder pain. Therefore, under the condition of paucity of data pertaining to north Indians, not only morphometric analysis of bicipital groove and a new definition of narrow/shallow groove to provide logical explanation for dependence of pathologies of biceps tendon on groove morphology is done but also a review of the literature has been carried out. Various dimensions such as lengths of medial and lateral walls, width, depth, medial wall, and opening angles including incidence of supratubercular ridge of bicipital groove from 101 humerii are 23 ± 5, 32 ± 5, 8 ± 2, 6 ± 1, 48.91 ± 10.31, 82.20 ± 22.62, and 37%, respectively. The average height along with average width of biceps tendon and average width along with average depth of bicipital groove from two cadavers are 1.8, 10.5, 11.3, and 5.5 mm, respectively. The knowledge of bicipital groove will be of paramount importance to anatomists for new data, for orthopaedic surgeons in carrying out surgical procedures in this region, and for physicians in the management of anterior shoulder pain in north Indian population.

Mathematical approximation of fibular malleolus curvature

While there are several manuscripts describing the articular surfaces of the ankle joint and the fibula itself, there is no study describing the outer surface and the degree of curvature of the fibular malleolus. This paper aims to approximate the sagital curvature of the outer surface of the lateral malleolus mathematically. Such data would facilitate the design of the anatomic plate that can be used for the ostheosynthesis of the fibular malleolus fracture. 30 males who were examined in the emergency department due to ankle sprains, where they underwent a standard anteroposterior x-ray of the ankle in the neutral position were recruited. The radiographs which revealed no bony injury were digitized and statistically processed. A mathematical function for each separate fibula was obtained through the processing of the digitized x-rays. When all the functions were applied to one graph, common traits of all fibulas were noted. The mean value of all functions was obtained and it corresponds to the polynomial function of degree 6. Mathematical approximation of the curvature is a simple and reliable method that can be applied to other ellipsoid human bone structures besides the ankle, thus being a valuable method in anthropometric, radiological and virtual geometric calculations.

Humeral head arthroplasty and its ability to restore original humeral head geometry

BACKGROUND

Modern prosthetic components are designed to enable restoration of proximal humeral morphology, provided that a precise osteotomy of the humeral head at the level of the anatomic neck is performed. To determine whether a simulated osteotomy and replacement arthroplasty with an idealized implant were able to restore original head geometry.

MATERIALS AND METHODS

A handheld digitizer and surface laser scanner were used to digitize 24 humeri. Computer models were used to simulate an osteotomy, performed at the anterior cartilage-metaphyseal interface, and reconstruct the head with a spherical prosthetic head. The head diameter, radius of curvature, and inclination and retroversion angles were calculated for each specimen and compared with the original humeral head.

RESULTS

The simulated osteotomy resulted in a 4.8° decrease in inclination (P < .01) and 11.3° increase in retroversion (P < .001). The radius of curvature in the coronal plane was not significantly different (P = .284). However, in the axial plane, the prosthesis was significantly larger than the original head for both head diameter (P < .001) and radius of curvature (P < .05).

DISCUSSION

The study suggests that the humeral head is not a perfect segment of a sphere and an osteotomy along the anterior cartilage-metaphyseal interface does not remove only the proximal humeral articular surface. Even with a fully adaptable prosthetic implant, replacement arthroplasty is not able to restore original head geometry.

CONCLUSIONS

Alterations to head geometry with the osteotomy described may alter the line of force through the prosthetic joint, producing eccentric loading at the glenoid, and contribute to early failure.

Cementless surface replacement arthroplasty of the shoulder for osteoarthritis: results of fifty Mark III Copeland prosthesis from an independent center with four-year mean follow-up

PURPOSE

Few studies have reported the outcome of cementless surface replacement (CSRA). We initiated this study to analyze results of the Mark III Copeland prosthesis used as a hemiarthroplasty in patients with glenohumeral osteoarthritis.

MATERIALS AND METHODS

We retrospectively reviewed 53 consecutive Mark III Copeland CRSA hemiarthroplasties in 46 patients (30 women, 16 men) with glenohumeral osteoarthritis from an independent institution by a single surgeon. Patients were a mean age of 69 years (range, 45-94 years). Mean follow-up was 4.2 years (range, 2-8 years). Fifty uncemented hemiarthroplasties were available for review.

RESULTS

Mean (range) age-adjusted Constant and Oxford scores improved from 38.5 (15-61) and 22 (9-31) to 75.1 (38-87) and 42 (18-48), respectively. Anterosuperior escape of the humeral head developed in 1 patient who had an oversized humeral component due to progressive rotator cuff failure at 2 years. Moderate glenoid erosion was present in 12% and correlated with oversizing of the humeral component. There was one revision to a stemmed cemented hemiarthroplasty for periprosthetic fracture. No patients have required revision for aseptic loosening, rotator cuff failure, or glenoid erosion to date.

CONCLUSIONS

Copeland surface replacement hemiarthroplasty for glenohumeral osteoarthritis can provide functional results similar to modular stemmed prostheses, with a relatively low revision rate at 4.2 years of follow-up; however, there is high rate of glenoid erosion that may complicate future revision surgery, and we did not achieve the same functional improvement as that achieved from the designer's institution.

Variability of medial and posterior offset in patients with fourth-generation stemmed shoulder arthroplasty

PURPOSE

Most anthropometric data on the proximal humerus has been obtained from deceased healthy individuals with no deformities. Endoprostheses are implanted for primary and secondary osteoarthritis, rheumatoid arthritis,humeral-head necrosis, fracture sequelae and other humeral-head deformities. This indicates that pathologicoanatomical variability may be greater than previously assumed. We therefore investigated a group of patients with typical shoulder replacement diagnoses, including posttraumatic and rheumatic deformities.

MATERIAL AND METHODS

One hundred and twenty-two patients with a double eccentrically adjustable shaft endoprosthesis served as a specific dimension gauge to determine in vivo the individual humeral-head rotation centres from the position of the adjustable prosthesis taper and the eccentric head.

RESULTS

All prosthesis heads were positioned eccentrically.The entire adjustment range of the prosthesis of 12 mm medial/lateral and 6 mm dorsal/ventral was required. Mean values for effective offset were 5.84 mm mediolaterally[standard deviation (SD) 1.95, minimum +2, maximum +11]and 1.71 mm anteroposteriorly (SD 1.71, minimum −3,maximum 3 mm), averaging 5.16 mm (SD 1.76, minimum +2,maximum + 10). The posterior offset averaged 1.85 mm(SD 1.85, minimum −1, maximum + 6 mm).

CONCLUSIONS

In summary, variability of the combined medial and dorsal offset of the humeral-head rotational centre determined in patients with typical underlying diagnoses in shoulder replacement was not greater than that recorded in the literature for healthy deceased patients.The range of deviation is substantial and shows the need for an adjustable prosthetic system.

A three-dimensional analysis of humeral head retroversion

INTRODUCTION

The anatomic neck of the humerus is used as a reference for the osteotomy in shoulder arthroplasty. Resection along the anterior portion of the cartilage/metaphyseal border is assumed to remove a cap of a sphere that can accurately be replaced with a spherical prosthetic implant oriented precisely to the original articular surface. The aim of this study was to determine the variability in retroversion of the cartilage/metaphyseal interface in the axial plane.

METHODS

Surface topography data for 24 arms from deceased donors were collected by using a hand-held digitizer and a surface laser scanner. Data were combined into the same coordinate system and graphically presented. The humeral head was divided into 6 sections in the axial plane and the retroversion angle measured at each level with reference to the transepicondylar axis at the elbow.

RESULTS

The mean retroversion of the humeral head at the midpoint between the superior and inferior margins was 18.6°. The angle increased as the position of the measurement moved superiorly to 22.5°. In contrast, the retroversion angle reduced as the position of measurement moved more inferiorly to 14.3°.

DISCUSSION

The results suggest that the cartilage/metaphyseal interface is not circular encompassing a spherical cap of a sphere. Furthermore, there appears to be a clockwise torsion of the cartilage/metaphyseal interface about the transverse axis from its medial to lateral aspect.

CONCLUSION

The cartilage/metaphyseal interface shows a degree of variability that makes it an unreliable landmark to perform an osteotomy when the anterior aspect of the interface is used.

Three-dimensional volume-rendering computed tomography for measuring humeral version

HYPOTHESIS

Humeral version is highly variable in human beings. Accurate assessment of humeral version may allow for more anatomic reconstruction at shoulder arthroplasty. Two-dimensional (2D) computed tomography (CT) has been used to measure humeral version but has limitations of poor interobserver reproducibility and strict dependence on arm positioning during image acquisition. This study evaluated a new technique, 3-dimensional (3D) volume rendering, for measuring humeral version.

MATERIALS AND METHODS

Eight dried human humerus specimens were included in the study. Gold standard measurements of humeral version were obtained by use of metallic beads and fluoroscopy. The specimens were then scanned at CT in 2 different positions, 1 neutral to the table and 1 angled at 20 degrees . The image data sets were used to measure humeral version in each bone with both the standard 2D technique and the new 3D technique. Measurements were performed by 3 readers at 2 different time points. Readers were blinded to the gold standard results and each others' measurements.

RESULTS

For all readers, 3D measurements averaged within 4.3 degrees of the gold standard. For 2 of the 3 readers, 3D measurements were more accurate than 2D measurements. For all 3 readers, intraobserver variability was better with the 3D technique. For all reader pairs, interobserver variability was better with the 3D technique.

CONCLUSIONS

This study shows a 3D volume-rendering CT technique to measure humeral version accurately and consistently that is independent of patient positioning.

Differences in reconstruction of the anatomy with modern adjustable compared to second-generation shoulder prosthesis

Reconstruction of the anatomy of the proximal humerus is a prerequisite to achieving good long-term clinical results after shoulder arthroplasty. Modern, adjustable prostheses have greater flexibility of inclination, retroversion, and medial and dorsal offset in comparison with older prostheses. Such improvements should allow for better reconstruction of the centre of rotation compared to older prostheses. Reconstruction of the humeral head centre was assessed in 106 modern adjustable (Affinis) and 47 second-generation prostheses. All reconstructions were compared both to the preoperative state and the unoperated shoulder. To describe the pre- and postoperative states, the geometry and position of the humeral head in relation to the glenoid were analysed on patient radiographs. Applying the defined parameters, modern adjustable prostheses showed better reconstruction than second generation prostheses. Parameter values measured in reconstructions using fourth generation prostheses were comparable to those of the unoperated shoulder, but differed significantly from the preoperative state. Second generation prostheses, in contrast, only show non-specific differences in parameter values. This suggests that an approximate reconstruction of normal anatomy can be achieved using a modern fourth generation prosthesis. Reconstruction of the complex anatomy of the proximal humerus is significantly better with modern adjustable prostheses compared to second generation prostheses. Improved clinical outcome can therefore be predicted in a functional and intact rotator cuff. The advantage of using modern prostheses systems over older models is clearly demonstrated in this study.

Effect of posterior offset humeral components on range of motion in reverse shoulder arthroplasty

The purpose of this study was to evaluate the effect of eccentric humeral components with different degrees of posterior offset on range of glenohumeral motion in reverse shoulder arthroplasty. Uncemented PROMOS® reverse shoulder prostheses were implanted in eight human cadaveric shoulder specimens. Passive range of motion was evaluated with a robot-assisted shoulder simulator. Three movements were tested: abduction, anterior elevation and external rotation. Each specimen was tested with a customary reverse humeral component and two eccentric components with 3 and 6 mm of posterior offset respectively. Mean abduction was 81° (standard deviation [SD] 12) for the customary reverse components, 81° (SD 13) for the 3 mm eccentric and 82° (SD 15) for 6-mm eccentric implants. Mean anterior elevation was 68° (SD 13) in the regular group and 66° (SD 14) and 63° (SD 14) for 3- and 6-mm eccentric groups. With all configurations, 90° of external rotation were achieved without requiring more than 2 N·m of applied rotational moment. Although there was no statistically significant difference between the conventional and the eccentric implants, anterior elevation was decreased by almost 20° in three of eight shoulders with the posterior offset configurations. This was due to a conflict between the proximal humerus and the anterior aspect of the acromion or the coracoid. Although eccentric humeral components can be useful in reverse shoulder arthroplasty to avoid anterior cortical defects in individuals with pronounced humeral head posterior offset, a potential conflict between proximal humerus and scapula may have an unfavourable effect on range of anterior elevation. However, this observation is only true for the uncemented PROMOS® reverse prosthesis. Other reverse shoulder designs with posterior offset components are yet to be tested.

Clinical and radiological follow-up of the Aequalis third-generation cemented total shoulder replacement

There are no long-term published results on the survival of a third-generation cemented total shoulder replacement. We describe a clinical and radiological study of the Aequalis total shoulder replacement for a minimum of ten years. Between September 1996 and May 1998, 39 consecutive patients underwent a primary cemented total shoulder replacement using this prosthesis. Data were collected prospectively on all patients each year, for a minimum of ten years, or until death or failure of the prosthesis. At a follow-up of at least ten years, 12 patients had died with the prosthesis intact and two had emigrated, leaving 25 available for clinical review. Of these, 13 had rheumatoid arthritis and 12 osteoarthritis. One refused radiological review leaving 24 with fresh radiographs.

Survivorship at ten years was 100% for the humeral component and 92% for the glenoid component. The incidence of lucent lines was low. No humeral component was thought to be at risk and only two glenoid components. The osteoarthritic group gained a mean 65° in forward flexion and their Constant score improved by a mean 41.4 points (13 to 55). The rheumatoid group gained a mean of 24° in flexion and their Constant score improved by 29.4 points. This difference may have been due to failure of the rotator cuff in 75% of the patients with rheumatoid arthritis.

Thus a third-generation total shoulder replacement gives an excellent result in patients with osteoarthritis and an intact rotator cuff. Patients with rheumatoid arthritis have a 75% risk of failure of the rotator cuff at ten years.

Prosthetic replacement for proximal humeral fractures

The ideal management of complex proximal humeral fractures continues to be debatable. Evolution of proximal humeral fracture management, during the past decade, led to the implementation of many innovations in surgical treatment. Even though the pendulum of treatment seems to swing towards new trends such as locked plating, hemiarthroplasty remains a valid and reliable option that serves the patient's needs well. Hemiarthroplasty is indicated for complex proximal humeral fractures in elderly patients with poor bone stock and when internal fixation is difficult or unreliable. Hemiarthroplasty provides a better result when it is performed early post-injury. Stem height, retroversion and tuberosity positioning are technical aspects of utmost importance. Additionally reverse total shoulder arthroplasty is an alternative new modality that can be used as a primary solution in selected patients with proximal humeral fracture treatment. Failed hemiarthroplasty and fracture sequelae can be successfully managed with reverse total shoulder arthroplasty. Individual decision-making and tailored treatment that takes into consideration the personality of the fracture and the patient's characteristics should be used.

CT scan method accurately assesses humeral head retroversion

Humeral head retroversion is not well described with the literature controversial regarding accuracy of measurement methods and ranges of normal values. We therefore determined normal humeral head retroversion and assessed the measurement methods. We measured retroversion in 65 cadaveric humeri, including 52 paired specimens, using four methods: radiographic, computed tomography (CT) scan, computer-assisted, and direct methods. We also assessed the distance between the humeral head central axis and the bicipital groove. CT scan methods accurately measure humeral head retroversion, while radiographic methods do not. The retroversion with respect to the transepicondylar axis was 17.9 degrees and 21.5 degrees with respect to the trochlear tangent axis. The difference between the right and left humeri was 8.9 degrees. The distance between the central axis of the humeral head and the bicipital groove was 7.0 mm and was consistent between right and left humeri. Humeral head retroversion may be most accurately obtained using the patient's own anatomic landmarks or, if not, identifiable retroversion as measured by those landmarks on contralateral side or the bicipital groove.

Comparison of anatomical shoulder prostheses and the proximal humeri of Chinese people

Reconstruction of normal anatomy is important to a successful proximal humeral arthroplasty, in which the surgeon needs to know multiple measured anatomical parameters during the surgery. Based on three-dimensional computed tomography scanning data, computer models of the proximal humeri of 180 Chinese people were built. They came from 77 males and 103 females; their ages ranged from 19 to 86 years. Anatomical parameters including the curvature diameter of the head, the head height, the inclination, and the retroversion were measured using the software in these three-dimensional proximal humerus models. The methodology was valid and the measured results showed marked variations in all those parameters. On average, the curvature diameter of the head was 44.6 mm, ranging from 36.4 to 55.5 mm. The head height was located at 16.7 +/- 1.9 mm (minimum, 12.4 mm; maximum, 22.0 mm). The inclination angle ranged from 122.35 degrees to 147.09 degrees (mean, 132.4 +/- 4.7 degrees). The proximal humeral retroversion was found to be extremely variable, ranging from -4.71 degrees to 52.46 degrees, and has a mean of 21.11 degrees. Then these measured results were compared with four commonly used anatomical prostheses. The wide range of variation in the normal values makes it difficult to restore anatomical characteristics individually. Thus, the use of an accurate three-dimensional model to guide surgery preoperatively can improve the outcome of some serious cases, such as gross degenerative change and large-bone-loss surgery.

Robotic cadaver testing of a new total ankle prosthesis model (German Ankle System)

BACKGROUND

An investigation was carried out into possible increased forces, torques, and altered motions during load-bearing ankle motion after implantation of two different total ankle prostheses. We hypothesized that the parameters investigated would not differ in relation to the two implants compared.

METHODS

We included two different ankle prostheses (Hintegra, Newdeal, Vienne, France; German Ankle System, R-Innovation, Coburg, Germany). The prostheses were implanted in seven paired cadaver specimens. The specimens were mounted on an industrial robot that enables complex motion under predefined conditions (RX 90, Stäubli, Bayreuth, Germany). The robot detected the load-bearing (30 kg) motion of the 100(th) cycle of the specimens without prostheses as the baseline for the later testing, and mimicked that exact motion during 100 cycles after the prostheses were implanted. The resulting forces, torques, and bone motions were recorded and the differences between the prostheses compared.

RESULTS

The Hintegra and German Ankle System, significantly increased the forces and torques in relation to the specimen without a prosthesis with one exception (one-sample-t-test, each p < or = 0.01; exception, parameter lateral force measured with the German Ankle System, p = 0.34). The force, torque, and motion differences between the specimens before and after implantation of the prostheses were lower with the German Ankle System than with the Hintegra (unpaired t-test, each p < or = 0.05).

CONCLUSIONS

The German Ankle System prosthesis had less of an effect on resulting forces and torques during partial weightbearing passive ankle motion than the Hintegra prosthesis. This might improve function and minimize loosening during the clinical use.

„Resurfacing“ des Humeruskopfes

Surface replacement arthroplasty of the shoulder offers the ability to restore anatomy and biomechanics of the glenohumeral joint, if sufficient humeral bone stock of at least 60% of the humeral head is preserved and no severe deformity is present. The implantation following the individual anatomy helps to avoid complications such as prosthetic malpositioning and periprosthetic fractures. While the use of a glenoid component is technically demanding, revision to a stem prosthesis is relatively easy because of bone stock preservation. Indications for humeral head resurfacing are osteoarthritis (OA), rheumatoid arthritis (RA), avascular necrosis stages 2-4, and stable forms of cuff tear arthropathy (CTA). Published results for OA and RA are comparable to those obtained with modern modular stem prostheses; the use in CTA appears promising under "limited goals criteria."

Improvements in survival of the uncemented Nottingham Total Shoulder prosthesis: a prospective comparative study

Background

The uncemented Nottingham Total Shoulder Replacement prosthesis system (Nottingham TSR) was developed from the previous BioModular^® shoulder prosthesis taking into consideration the causes of the initial implant's failure.

We investigated the impact of changes in the design of Nottingham TSR prosthesis on its survivorship rate.

Methods

Survivorship analyses of three types of uncemented total shoulder arthroplasty prostheses (BioModular^®, initial Nottingham TSR and current Nottingham TSR systems with 11, 8 and 4 year survivorship data respectively) were compared. All these prostheses were implanted for the treatment of disabling pain in the shoulder due to primary and secondary osteoarthritis or rheumatoid arthritis. Each type of the prosthesis studied was implanted in consecutive group of patients – 90 patients with BioModular^® system, 103 with the initial Nottingham TSR and 34 patients with the current Nottingham TSR system.

The comparison of the annual cumulative survivorship values in the compatible time range between the three groups was done according to the paired t test.

Results

The 8-year and 11-year survivorship rates for the initially used modified BioModular^® uncemented prosthesis were relatively low (75.6% and 71.7% respectively) comparing to the reported survivorship of the conventional cemented implants. The 8-year survivorship for the uncemented Nottingham TSR prosthesis was significantly higher (81.8%), but still not in the desired range of above 90%, that is found in other cemented designs. Glenoid component loosening was the main factor of prosthesis failure in both prostheses and mainly occurred in the first 4 postoperative years. The 4-year survivorship of the currently re-designed Nottingham TSR prosthesis, with hydroxylapatite coating of the glenoid baseplate, was significantly higher, 93.1% as compared to 85.1% of the previous Nottingham TSR.

Conclusion

The initial Nottingham shoulder prosthesis showed significantly higher survivorship than the BioModular^® uncemented prosthesis, but lower than expected. Subsequently re-designed Nottingham TSR system presented a high short term survivorship rate that encourages its ongoing use

Reconstructing proximal humeral fractures using the bicipital groove as a landmark

Controversy persists in the literature regarding the use of the bicipital groove as an anatomic landmark to restore humeral head retroversion when treating complex proximal humeral fractures with arthroplasty. We quantified the three-dimensional geometry of the bicipital groove in 49 dried humeri relative to the intramedullary axis, quantified the reliability of using the bicipital groove as an anatomic landmark, and compared this reliability with that of the conventional technique that uses a fixed, average angle relative to the epicondylar axis to establish humeral head retroversion. The data show the anterior offset of the bicipital groove is nearly constant from proximal (7.3 mm +/- 2.8 mm) to distal (7.2 mm +/- 1.5 mm) relative to the intramedullary axis. Given the consistency, the distal bicipital groove (at the level of the surgical neck) is a reasonable landmark to establish humeral head retroversion after complex proximal humeral fractures having reliability (angular error of 7.9 degrees +/- 5.8 degrees) as good as or better than the conventional fixed-angle technique.

An anthropometric study of the bilateral anatomy of the humerus

The purpose of this study was to describe the extramedullary humeral morphology in paired humeri to determine whether geometric differences exist from side to side in the same individual. The anatomic characteristics of 28 paired, dry cadaveric humeri were measured by use of an electromagnetic tracking system. Of the characteristics examined, only the humeral head height was significantly different between right and left humeri in the same individual (P < .005). Most of the characteristics had excellent intra-specimen repeatability. In conclusion, there are few significant differences between contralateral humeral anatomic characteristics. Therefore, the uninjured contralateral humerus can provide a reasonable approximation to the native geometry of the fractured humerus and should be a reliable model for measuring parameters related to implant geometry and optimal positioning during hemiarthroplasty for the treatment of proximal humeral fractures.

Developments in shoulder arthroplasty

Indications for shoulder arthroplasty are numerous, mainly owing to glenohumeral osteoarthritis, rheumatoid arthritis, or fracture of the proximal humerus. However, the anatomy and the biomechanics of the shoulder are complex and shoulder arthroplasty has evolved significantly over the past 30 years. This paper presents the main recent evolutions in shoulder replacement, the questions not answered yet, and the main future areas of research. The review focuses firstly on the design, positioning, and fixation of the humeral component, secondly on the design, positioning, and fixation of the glenoid implant, and thirdly on other concepts of shoulder arthroplasty such as the reversed prosthesis, the cementless surface replacement arthroplasty, and the bipolar arthroplasty. This review demonstrates that more research is needed. Although, in the long term, large randomized trials are needed to settle the fundamental questions of what type of replacement and which kind of fixation should be used, biomechanical research in the laboratory should be focused primarily on the comprehension of glenoid loosening, which is a major cause of total shoulder arthroplasty failure, and the significance of radiolucent lines which are often seen but with no clear understanding about their relation with failure.

Early versus late mobilization after hemiarthroplasty for proximal humeral fractures

This randomized controlled trial compares 2 mobilization regimens after shoulder hemiarthroplasty for acute 3- and 4-part fractures. The aim was to establish whether the length of immobilization plays a role in the functional outcome, tuberosity healing, and subsequent range of motion. The same prosthesis and surgical technique were used. We recruited 59 patients into the study; 31 were randomized to early (2 weeks) mobilization and 28 to late (6 weeks) mobilization. Greater tuberosity migration was assessed with a series of radiographs, and the functional outcome was assessed with the Constant Shoulder Assessment and Oxford shoulder scores. Of the patients, 49 (mean age, 70 years) met the inclusion criteria and were followed up for 12 months. Greater tuberosity migration occurred in 3 cases in the early mobilization group and once in the late mobilization group (P > .10). There was no significant difference in the Constant Shoulder Assessment and Oxford scores between the 2 groups. Although there was a decreased incidence of tuberosity migration in the group undergoing late mobilization, this was not statistically significant.

Proximal humerus fractures

Proximal humerus fractures are common injuries. Knowledge of local anatomy is paramount in the evaluation and treatment of these injuries. Information regarding humeral head vascularity, fracture patterns, bone quality, and overall geometry have direct implications for nonoperative treatment, internal fixation, and hemiarthroplasty. The ascending branch of the anterior circumflex artery perfuses most of the humeral head. When fractured, the greater tuberosity tends to displace posterosuperiorly, the lesser tuberosity and the shaft displace medially, and the head may be pulled by the attached tuberosity, impacted into valgus, or in more severe cases dislocated, impacted, or divided. Internal fixation of two-part, three-part, and selected four-part fractures may be compromised by local osteopenia; knowledge of the location of the strongest bone in the proximal humerus combined with the use of fixed-angle devices and occasionally bone graft or substitutes has improved the outcome of osteosynthesis. When the humeral head cannot be preserved, successful hemiarthroplasty requires tuberosity union and anatomic restoration of the overall geometry of the proximal humerus in terms of height, retroversion, and head-tuberosity relationships.

Outcome of Copeland surface replacement shoulder arthroplasty

We report the outcome of humeral head surface replacement hemiarthroplasty performed at our institution using the Copeland prosthesis. We followed 56 shoulders (52 patients) for a mean of 34.2 months (range, 24-63 months). Two were lost to follow-up, and there were six deaths unrelated to the shoulder surgery. Preoperative diagnoses in the remainder were osteoarthritis (20), rheumatoid arthritis (26), rotator cuff tear arthropathy (1), and post-traumatic arthrosis (1). The mean age was 68 years. Constant scores for the whole group improved from a mean preoperative score of 16.4 (range, 8-36) to 54.0 (range, 20-83) at last follow-up (P < .05). Three cases underwent subsequent arthroscopic subacromial decompression for impingement symptoms. One case required revision for aseptic loosening to a stemmed implant. Contained, nonprogressive osteolysis was seen in 2 cases. One periprosthetic humeral neck fracture was managed successfully nonoperatively. These results are comparable to those obtained with a modern stemmed hemiarthroplasty and are similar to Copeland's own series.