Wednesday, May 25, 2016

Our infectious disease expert is tops

As many of our readers know, Paul Pottinger is one of the foremost experts in infectious diseases - especially in the challenging problem of periprosthetic infections of the shoulder (see this post).
What you may not know is that he is also an accomplished alpinist. On May 20 this photo was taken of him on the summit of Mount Everest. Being a bit superstitious, we did not want to post and toast to his success until he was safely back at base camp and now he is!
Congratulations, Paul!

Thursday, May 19, 2016

Long stem reverse total shoulder to the rescue

A middle aged patient sustained a proximal humeral fracture that was treated elsewhere with a humeral prosthesis as shown below. Note the absence of the greater tuberosity in this reconstruction indicating cuff deficiency.

As a result of this cuff deficiency the humeral head migrated superiorly and the patient developed pseudo paralysis.

A reverse total shoulder was placed, but there was difficulty in clearing the distal cement, so a short stem prosthesis was placed.

The humeral stem loosened.

We revised this arthroplasty using a 6mm diameter long stem prosthesis inserted after drilling the canal with a flexible reamer placed over a bulb-tipped guide wire. The fixation was excellent. Note the slight 'flex' in the prosthetic stem. 

Monday, May 16, 2016

What is a 'good' result after a joint replacement arthroplasty and how it can it be predicted?

Age and Preoperative Knee Society Score Are Significant Predictors of Outcomes Among Asians Following Total Knee Arthroplasty.

While this paper is about knees, its substance is relevant to important questions about shoulder arthroplasty: what is a good result and how can it be predicted?

These authors extracted registry data from 2006 to 2010. Outcomes were evaluated using the Oxford Knee Score (OKS)(higher scores indicate greater disability) and the Short Form (SF)-36 physical component summary (PCS)(higher scores indicate better physical function). Follow-up data were available for 3,062 patients who underwent primary TKA (mean age of 66.4 years; 79.5% female).

A "good outcome" at 5 years was defined in two ways:
(1) as an improvement in scores of greater than or equal to the minimal clinically important difference (MCID) in the primary analysis. The MCID for the OKS was 5, and the MCID for the PCS was 10. 
(2) as an OKS of <30 and a PCS score of >50. 

Age and preoperative Knee Society score (KSS) were found to be significant predictors. 

When outcomes were assessed by the MCID, lesser age and lower (worse) preoperative KSS predicted a good outcome at 5 years. 

When outcomes were assessed by absolute criteria (postoperative scores measured against OKS and PCS thresholds), a higher (better) preoperative KSS predicted a good outcome at 5 years. The effect of age was not significant.

Body mass index, preoperative flexion range, SF-36 mental component summary (MCS) score, mechanical alignment, sex, education level, ethnicity, operative side, number of comorbidities, type of anesthesia, and type of implant were found not to be significant predictors.

The authors concluded that the majority (85%) of their patients with osteoarthritis had good outcomes according to the MCID criterion and benefitted from primary TKA.

Older patients with a lower (worse) preoperative KSS can be informed that they have a high likelihood of improvement but a lower likelihood of achieving as good a functional outcome as those with better scores.

Comment: This paper is informative.
First, many of the factors that one might think would infuence the quality of the result did not have a significant effect (BMI, preoperative flexion range, SF-36 mental component summary (MCS) score, mechanical alignment, sex, education level, ethnicity, operative side, number of comorbidities, type of anesthesia, and type of implant).

Second, they showed that patients who were more functional before surgery realized the best function after surgery, whereas those who were less functional before surgery realized the most improvement.

These outcomes can be emulated by the chart below that uses data for three hypothetical patients.

We will all agree that the patient represented by the circle did poorly (as would be the case for any patient below the line). But did the diamond patient or the square patient get the better result? The diamond patient improved more but the square patient wound up with 90% of normal function and improved by half of the preoperative functional deficit (whereas the diamond improved only 33% of the preoperative functional deficit).

Rather than arguing whether the amount of improvement or the absolute value of the postoperative function is better, we should acknowlege that both may be useful in explaining the likely result of surgery to the patient.


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'

How do rotator cuff tears influence shoulder motion?

These authors studied 14 patients with rotator cuff tears and 14 healthy individuals with 35 reflective markers on the trunk and upper limb tracked by an optoelectronic system to measure the scapulohumeral rhythm (the ratio of glenohumeral to scapulothoracic motion in arm elevation) while the subjects carried out 5 comfortable scapular plane maximal arm elevations. They found a value of 3.9 for healthy controls.

Patients were separated by maximal arm elevation of 85° (category A) and 40° (category B). 

The mean scapulohumeral rhythm ratio during arm elevation was 2.8 for patients in category A; these patients  had a relatively consistent pattern as shown below with much lower values than controls (that is relatively less glenohumeral movement and relatively more scapulothoracic motion).  

The patients with only 40 degrees of active motion (Group B) had widely varying patterns of motion as shown below

The authors concluded that patients who reached at least 85° compensated for the loss of glenohumeral motion by increased scapulothoracic contribution.  
In contrast, patients who had less active range of motion had less contribution from scapulothoracic motion.

Comment: This study demonstrates that some patients with cuff deficiency can compensate by increasing the scapulothoracic contribution to active motion. There were only seven patients in each group and we are not presented with the cuff tear sizes in the two groups.

In our management of individuals with chronic cuff tears we encourage them to try a simple exercise program that encourages use of both the glenohumeral and scapulothoracic musculature (shown below)
It is interesting that some patients sent to us for consideration of reverse total shoulders because of apparent pseudoparalysis are able to regain substantial function with this simple exercise.


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'

Sunday, May 15, 2016

3D image intensifier navigation of K-wire placement in the glenoid - statistical vs clinical significance

Improved accuracy of K-wire positioning into the glenoid vault by intraoperative 3D image intensifier-based navigation for the glenoid component in shoulder arthroplasty

These authors hypothesized that navigated k-wire placement is more accurate and shows a smaller deviation angle to the standard centerline compared to the classical “free hand technic” in thirty-four pairs of fresh female sheep scapulae

We include some details of the method:
First, the shoulders from the navigated group 1 were mounted onto the operating table in the upright position. A small incision wasmade in the area of the scapular spine and a carbon-clamp withthree tracking points was fixed. A preoperative scan was performed with Ziehm VisionFD Vario 3D. The middle of the scanner was placed at the central point of the glenoid. The scan performed consisted of 110 single images witha radius of 136◦within 110 seconds. The DICOM-format raw datawere consequently transferred from the 3D image converter to theVectorVision©navigation system. In the navigation system, the data record was used as a CT data record. After creating a 3D image, the data was verified by comparing the image and the anatomy. This control was performedat three defined points (proximal glenoid, central glenoid and the distal glenoid).The instruments were calibrated using the instrument calibration matrix. A 1.8-mm navigable drill sleeve was used. By using the navigation screen, the wire wasplaced as centrally as possible. Subsequently, a K-wire was positioned and shortened to fit into the glenoid. 
In the freehand group 2, the shoulders were stabilized in the upright positionon the operating table. In contrast to group 1, the central point of theglenoid vault was determined visually using electrocauterization. Subsequently, drilling was also performed with the same navigable 1.8 mm sleeve in a perpendicular direction to the glenoid face planeand marked with a K-wire.

 The relation to glenoid standard and alternative centerlines (CL) and the position within the glenoid vault were analyzed.

In groups 1 and 2 the angle between the K-wire and standard CL was 2.2° and 4.7°, respectively (P = 0.01). The angle between the K-wire and alternative CL was 14.4° for group 1 and 17.2° for group 2 (P = 0.02). More navigated K-wire positions were identified within a 5 mm corridor along the glenoid vault CL (52 vs. 39; P = 0.004).

Comment: This article represents yet another method for placing a K-wire in the scapula, ostensibly to guide the preparation of the glenoid for glenoid component placement.

We do not know the cost and time for implementing this approach, whether it would be applicable in the clinical situation or whether the improvement of three degrees would lead to better results for patients than other methods.

As is well know to the readers of this blog, we do not use a guide wire, intaoperative imaging, or patient specific instrumentation to guide the reaming of the glenoid. By contrast (as shown in "D" below), we position a nubbed reamer without a guide wire so that the minimal amount of bone is removed without an attempt to 'correct' glenoid version. Using this method and soft tissue balancing without or with an anteriorly eccentric humeral head component (see this link), we have yet to experience problems with posterior instability or glenoid component failure. In this nice figure from Dr Lippitt, one can see some other approaches and their potential downsides.

Is the Propionibacterium in my skin today the same that was there previously?

Temporal Stability of the Human Skin Microbiome.

This article addresses a topic important for shoulder surgeons and their patients. Propionibacterium is the most common organism found at surgical revision of failed shoulder surgery. The source of these organisms is the patient's skin (dermal sebaceous glands). These investigators found that the strains of skin microbes (bacteria, fungi, and viruses) are shaped by the host's physiology and are stable over time in spite of the external exposures shown in this cartoon.

Their abstract: "Biogeography and individuality shape the structural and functional composition of the human skin microbiome. To explore these factors' contribution to skin microbial community stability, we generated metagenomic sequence data from longitudinal samples collected over months and years. Analyzing these samples using a multi-kingdom, reference-based approach, we found that despite the skin's exposure to the external environment, its bacterial, fungal, and viral communities were largely stable over time. Site, individuality, and phylogeny were all determinants of stability. Foot sites exhibited the most variability; individuals differed in stability; and transience was a particular characteristic of eukaryotic viruses, which showed little site-specificity in colonization. Strain and single-nucleotide variant-level analysis showed that individuals maintain, rather than reacquire, prevalent microbes from the environment. Longitudinal stability of skin microbial communities generates hypotheses about colonization resistance and empowers clinical studies exploring alterations observed in disease states."

Both P. acnes and Propionibacterium phage (the virus associated with it) are abundant in sebaceous sites (such as the shoulder, chest and back). They observed a strong anti correlation in sebaceous communities that contain both P. acnes and its phage; this anti-correlation together with the observed phage-host dynamics over time suggests antagonism (see the green graph below). Note the abundance of both the Propi phage and Propi in the sebaceous areas.

They found that individuals have distinct microbial SNV signatures that are stable over time across body sites for time periods of a year (see figure below). Temporal stability, short- or long-term, surpassed the similarity between individuals, indicating that P. acnes stability likely derives from maintaining an individual’s strains over time and less from the acquisition of new strains from the environment or other individuals. "B" shows the relative abundance plots for different strains of Propi for the chest of three different individuals.

The authors surmise that despite the continuous perturbation that human skin undergoes in daily life and in the absence of major perturbations, dominant characteristics of skin microbial communities would remain stable indefinitely as is the case for gut communities. However, extrinsic perturbations (probiotics, prebiotics, antimicrobials, antibiotics, long-term environmental relocations, diet, immunosuppression, illness, or the occurrence of disease) can alter the skin microbiota. Do these changes make a person more or less likely to acquire Propionibacterium in and around their shoulder arthroplasty components?

Can the Propi Phage virus be used to treat Priopi infection, as suggested by Ian Whitney (see link)(one of our past shoulder fellows)?

The loose glenoid component - a challenge

Aman in his 60s had a history of multiple prior procedures on the left shoulder including multiple arthroscopic subacromial decompressions, hemiarthroplasty, repair of subscapularis failure, leading to a total shoulder arthroplasty in 2006 - the shoulder was never really comfortable after that. Because of increasing pain requiring narcotic medication he presented in 2015 with no systemic signs of infection. He  had maintained good range of motion and his main complaint is pain, which is worse with overhead movement but also present with rest and at night. He had crepitus with movement particularly reaching overhead. He had no fever, chills, or wound drainge. He had had a previous workup for infection including a bone scan which was negative.

On his AP view one can see the superior placement of the humeral head relative to both the humeral tuberosity (see this prior post) and the glenoid.

Aseptic loosening of the glenoid was suspected; he desired an exploration of the shoulder. The joint fluid was clear and there was no gross evidence of infection. The subscapularis was scarred. The rotator cuff was intact. The humeral component was solidly fixed in the humerus. The head was proud superiorly. The glenoid component was grossly loose and was removed. The stem was tightly fixed and could not be removed without humeral osteotomy; because of the absence of apparent infection, it was left in place. The head was replaced  with one that was inferiorly eccentric to better align with the tuberosity and glenoid. 

He was placed on the yellow protocol (see this link). His culture results were:

Collar membrane:

 Glenoid membrane:
 Glenoid explant:
 Joint fluid:

With these culture results he was converted to the red protocol (see this link).
While on antibiotics his shoulder was comfortable and functional.

Six months after revision, the shoulder appeared stable.

However, after discontinuance of his antibiotics, the symptoms recurred, including pain in the humerus were the stem had been retained. Note the slots in the distal prosthesis and the tight fit of the stem in the diaphysis.

The patient desired another revision with stem removal to manage the potential for residual bacteria in a biofilm on the retained component.

The humeral body was extremely well fixed with substantial bone growth into the slots. An extensive humeral osteotomy was required. The shoulder showed no obvious evidence of infection. Vigorous debridement and irrigation was followed by a bodice repair (see this link) after a long stem prosthesis had been inserted. 

The patient is currently on the red protocol with the plan for lifetime antibiotics.

Comment: This case shows the challenges of decision making in the management of an apparently aseptic case of glenoid loosening.

Consultation for those who live a distance away from Seattle.

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