Saturday, February 17, 2018

Surgically prepared skin is not sterile

Preoperative Skin-Surface Cultures Can Help to Predict the Presence of Propionibacterium in Shoulder Arthroplasty Wounds

These authors point out that propionibacterium species are commonly cultured from specimens harvested at the time of revision shoulder arthroplasty. These bacteria reside in normal sebaceous glands, out of reach of surgical skin preparation. The arthroplasty incision transects these structures, which allows Propionibacterium to inoculate the wound and to potentially lead to the formation of a biofilm on the inserted implant.

To help identify patients who are at increased risk for wound inoculation, they investigated whether preoperative cultures of the specimens from the unprepared skin surface were predictive of the results of intraoperative cultures of dermal wound-edge specimens obtained immediately after incision of he surgically prepared skin.

Sixty-six patients (mean age, 66.1 ± 9.4 years [range, 37 to 82 years]; 73% male) undergoing primary shoulder arthroplasty had preoperative cultures of the unprepared skin surface and intraoperative cultures of the freshly incised dermis using special culture swabs.

For the first 50 patients, a control swab was opened to air during the same time that the dermal specimen was obtained.

The results for female and male patients were characterized as the Specimen Propionibacterium Value (SpPV) (see this link). They then determined the degree to which the results of cultures of the skin surface specimens were predictive of the results of culture of the dermal specimens.

The skin-surface SpPV was ≥ 1 in 3 (17%) of the 18 female patients and 34 (71%) of the 48 male patients (p <0.001). The dermal SpPV was  ≥ 1 in 0 (0%) of the 18 female patients and 19 (40%) of the 48 male patients (p < 0.001).

None of the control samples had an SpPV of  ≥ 1  The predictive characteristics of a skin-surface SpPV of  ≥ 1 for a dermal SpPV of  ≥ 1 were as follows: sensitivity, 1.00 (95% confidence interval [CI], 0.82 to 1.00); specificity, 0.62 (95% CI, 0.46 to 0.75); positive predictive value, 0.51 (95% CI, 0.34 to 0.68); and negative predictive value, 1.00 (95% CI, 0.88 to 1.00).

A preoperative culture of the unprepared skin surface can help to predict whether the freshly incised dermal edge is likely to be positive for Propionibacterium. This test may help to identify patients who may merit more aggressive topical and systemic antibiotic prophylaxis.

This study shows that surgeons have the opportunity to use preoperative skin cultures to determine the likelihood that the shoulder arthroplasty wound will be culture-positive for Propionibacterium.

Comment: This study is important for at least four reasons: (1) when the skin is incised for a shoulder arthroplasty, the freshly cut dermal edge is often culture positive for Propionibacterium in spite of IV antibiotics and surgical skin preparation, (2) it is important that each surgeon know his/her rate of positive control cultures to better inform the interpretation of deep wound cultures, (3) the semiquantitative results of cultures appear to be more useful than simply reporting a culture as 'positive or negative', and (4) cultures of the unprepared skin surface can be predictive of the results of cultures of the freshly incised dermis.
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Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

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Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and runreverse total shoulderCTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

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Wednesday, February 14, 2018

What is stress shielding?

Stress shielding of the humerus in press-fit anatomic shoulder arthroplasty: review and recommendations for evaluation

Stress shielding has been defined as "Osteopenia occurring in bone as the result of removal of normal stress from the bone by an implant"

These authors point out that a wide variety of humeral implants and implant fixation methods are now available, each of which has the potential for changing the distribution of loads applied to the humerus. Over time, changes in load distribution can be expected to produce changes in the bone - some areas will developed increased density while others will loose bone density. These changes are commonly referred to as 'stress shielding'. The clinical effects of stress shielding (symptoms, risk of fracture, etc) are not well documented.

In this report the authors review the current literature on press-fit fixation of the humeral component during total shoulder arthroplasty and propose minimum requirements for radiographic descriptions of stress shielding of the humeral component during total shoulder arthroplasty and propose minimum requirements for radiographic descriptions of stress shielding.

Signs of stress shielding are thought to include cortical thinning, osteopenia, spot welds, and condensation lines. The challenge is that each of these is not an 'all or none' characteristic; each has at least 50 shades of grey. The authors offer these two examples of medial calcar osteolysis (blue arrow) 2 years after a total shoulder arthroplasty and osteopenia and proximal lateral cortical thinning (green arrow) 2 years postoperatively.


 
 







The challenges in diagnosing 'stress shielding' are (1) the radiographic appearance can be altered by the technique of the X-ray

 

(2) it is difficult to determine the degree to which the findings were present prior to the arthroplasty and 
(3) characteristics like cortical thinning and osteopenia are difficult to quantitate on plain films.

We conclude that diagnosing the presence and degree of  'stress shielding' can be a challenge.

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Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

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Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and runreverse total shoulderCTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

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How to track progress of patients having a ream and run when they live over 1,000 miles away

For us, the key to closely following patients after the ream and run is the 'lateral supine photo'.
Here are three examples

1 day post op after second side ream and run (first done 6 months ago) - 2018 miles away

1 day post op after second side ream and run (first done 3 years ago) - 2327 miles away

3 weeks post op - 1438 miles away
                                   

The point is that with this simple photo - which can be sent by cell phone - we can track progress and make changes in the rehabilitation program as needed. With this approach, the distance becomes irrelevant.

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Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

Click here to see the new Rotator Cuff Book

Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and runreverse total shoulderCTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

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Tuesday, February 13, 2018

Glenoid component loosening

Sequential 3-dimensional computed tomography analysis of implant position following total shoulder arthroplasty

These authors used  3-dimensional computed tomography (CT) to evaluate glenoid component position over time in 20 patients with minimum 2-year follow-up. They obtained scans (1) before surgery, (2) within two weeks after surgery and (3) at a minimum of 2-years after surgery.

Glenoids with evidence of component shift and/or central peg osteolysis were considered at risk of loosening. 

Of the patients, 7 (35%) showed evidence of glenoid components at risk of loosening, 6 with component shift (3 with increased inclination alone, 1 with increased retroversion alone, and 2 with both increased inclination and retroversion). 

Significantly more patients with glenoid component shift had central peg osteolysis compared with those without shift (83% vs 7%, P = .002).



Comment: It is surely of concern that more than one third of these patients having total shoulder arthroplasty were characterized as being at risk for glenoid component loosening.

Some of the findings in the Table S1 were interesting:
Type A glenoids tended to be at increased risk for loosening:
    Of 11 type A glenoids, 4 were at risk for loosening.
    Of 7 type B or C glenoids, only 1 was at risk for loosening.

Posteriorly augmented glenoid components tended to be at increased risk for loosening:
    Of 14 standard glenoid components, 4 were at risk for loosening
    Of 6 posteriorly augmented glenoid components, 3 were at risk for loosening.

Retroverted glenoids tended to at lower risk for loosening.

While these differences did not attain statistical significance with the small number of cases, these trends merit further observation in that they challenge some of the commonly held tenets.

The increases in inclination noted are of interest as well. Perhaps they were related to cuff failure allowing the humeral head to migrate upwards resulting in the rocking horse phenomenon. Loading of the superior glenoid can also result from superior positioning of the humeral component.

Here are some of their findings as seen on plain films. Note the narrowed acromiohumeral interval on the 'at risk glenoid' on the left.




Finally, this study requires each patient to have three CT scans, imaging that comes at a cost in terms of dollars and in terms of radiation exposure to the patient.

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Healing through joint replacement

Supporting progress in shoulder surgery

Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

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Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

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Short humeral stem - varus loosening

An avid golfer presented to us 2 years after a right total shoulder performed at another institution. While never comfortable after the initial surgery, the pain in the arm had been steadily increasing. The AP x-ray showed the humeral component had migrated into various with ballooning of the lateral humeral cortex.


At surgery we are able to bypass the weakened portion of the humerus with a standard stem fixed with impaction allograft, as shown below.




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Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

Click here to see the new Rotator Cuff Book

Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and runreverse total shoulderCTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

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When is a total shoulder "successful"?

Quantifying success after total shoulder arthroplasty: the substantial clinical benefit

These authors state that the term "minimal clinically important difference" (MCID) describes the minimum value for meaningful improvement, whereas "substantial clinical benefit" (SCB) describes the value for substantial improvement  

At the latest follow-up for their patients having total shoulder arthroplasty, each patient was asked to rate their shoulder as “worse,” “unchanged,” “better,” or “much better” relative to his or her preoperative condition.

They quantified the SCB as the minimum difference in preoperative-to-postoperative outcome that resulted in a patient describing his or her treatment as “much better” compared with “worse” or “unchanged” for 1,568 shoulder arthroplasties with 2-year minimum follow-up performed by  13 shoulder surgeons.

The anchor-based SCB results were American Shoulder and Elbow Surgeons score, 31.5 ± 2.0; Constant Score, 19.1 ± 1.7; University of California Los Angeles Shoulder Rating Scale score, 12.6 ± 0.5; Simple Shoulder Test score, 3.4 ± 0.3; Shoulder Pain and Disability Index score, 45.4 ± 2.2; global shoulder function, 3.1 ± 0.2; visual analog scale, 3.2 ± 0.3; active abduction, 28.5° ± 3.1°; active forward flexion, 35.4° ± 3.5°; and active external rotation, 11.7° ± 1.9°. 

Two-thirds of patients achieved the SCB threshold after TSA. Generally, a change of 30% of the total possible score for each outcome metric approximates or exceeds this SCB threshold. 


Comment: As we've pointed out previously, the problem with an anchor question, such as "is your shoulder“worse,” “unchanged,” “better,” or “much better” relative to your preoperative condition?" is that it assumes the patient accurately recalls their preoperative condition years later. In this study the time between the preoperative condition and the posing of the question was long: the average follow-up was 44.9 ± 23.8 months (range, 24- 157 months), with an average follow-up of 49.7 ± 27.5 months for aTSA patients and 40.2 ± 18.6 months for rTSA patients.

It seems more robust to document the preoperative and postoperative scores and then express the improvement as a percent of maximal possible improvement (rather than as a percent of the total possible score.

For example the SCB for the Simple Shoulder Test was determined to be 3.4 . Thus an improvement of 4 would be considered a 'successful' outcome. However, an improvement from 0 to 4 is not likely to make the patient as happy with the outcome as an improvement from 7 to 11. The improvement from 0 to 4 represents a change of 33% of the maximal possible improvement, while an improvement from 7 to 11 would represent a change of 80% of the maximal possible improvement.

See this related post:

Quantifying success after total shoulder arthroplasty: the minimal clinically important difference 

These authors sought to define a minimal clinically important difference (MCID) for different shoulder outcome metrics and range of motion after total shoulder arthroplasty (TSA) in 466 anatomic TSA (aTSA) and reverse TSA (rTSA) using an anchor-based method: asking the patient to rate his or her shoulder as “worse,” “unchanged,” “better,” or “much better” relative to the preoperative condition.

The anchor-based MCIDs were
Simple Shoulder Test score = 1.5 ± 0.3
American Shoulder and Elbow Surgeons = 13.6 ± 2.3
Constant score = 5.7 ± 1.9
University of California Los Angeles Shoulder Rating Scale = 8.7 ± 0.6
Shoulder Pain and Disability Index score = 20.6 ± 2.6
Global shoulder function = 1.4 ± 0.3
Pain visual analog scale = 1.6 ±  0.3
Active abduction = 7° ±  4°
Active forward flexion = 12° ± 4°
Active external rotation = 3° ± 2°. 

Female gender and rTSA were associated with lower MCID values compared with male gender and aTSA patients.

Comment: There are two important limitations to such a study. 
First, the patients' answer to the anchor question requires them to recall the condition of their shoulder prior to their surgery a long and variable time ( 44.9 ± 23.8 months (range, 24-157)) prior to the last followup.

Second, the concept of the MCID does not consider that the absolute amount of improvement (e.g. the MCID of 1.5 for the Simple Shoulder Test), may be less important than the amount of improvement expressed as a percent of the maximal possible improvement (I/MPI).

For example an improvement in the SST score by the MCID of 1.5 from a preoperative score from 0 out of 12 to a postoperative score of 2 out of 12 is an improvement of only 2/12ths or only 17% of the maximal possible improvement. Patients with a postoperative SST of 2 are rarely satisfied with the outcome of their arthroplasty (even though they improved by the MCID).
On the other hand, an improvement in the SST score by the MCID of 1.5 from a preoperative score from 8 out of 12 to a postoperative score of 10 out of 12 is an improvement of 50% of the maximal possible improvement  (2/4).

Using the SST, this study showed highly respectable average I/MPI of 80% for anatomic total shoulders and an average I/MPI of 76% for reverse total shoulders.

The percentage of maximal possible improvement in the SST is easy to calculate and easily understood by patients.


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Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

Click here to see the new Rotator Cuff Book

Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and runreverse total shoulderCTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

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Monday, February 12, 2018

Failure of the glenoid component in total shoulder arthroplasty

What can be learned from an analysis of 215 glenoid component failures?

These authors sought to identify surgeon-controlled factors contribute to glenoid component failure.

They reviewed the clinical and radiographic features of 215 total shoulder arthroplasties that they revised for symptomatic glenoid component failure. These patients had poor patient self-assessed shoulder function (mean Simple Shoulder Test score, 3.0 ± 2.7).
These shoulders often showed multiple failure modes; 72% had glenoid component loosening, 69% had polyethylene wear, 51% had glenohumeral decentering, and 25% had humeral component loosening. Metal-backed/hybrid and keeled glenoid designs were more likely to demonstrate loosening, malposition, dislocation, and early failure in comparison to pegged designs. 

Glenoid components with cement on the backside were more prevalent among those having revisions within five years of the index arthroplasty.

Some of the identified failure modes are exemplified in these figures









The authors suggest that the occurrence of severe glenoid component failure might be reduced by paying attention to glenoid component design (all polyethylene, pegged fixation) and insertion technique (excellent seating without backside cement), restoring the normal balance of the humeral head in the center of the glenoid (soft tissue balancing and proper component placement), and considering a reverse total shoulder when the shoulder is unstable because of soft tissue deficiency.

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The reader may also be interested in these posts:



Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

Click here to see the new Rotator Cuff Book

Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and runreverse total shoulderCTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

See the countries from which our readers come on this post.