Applying the Deltoid Tuberosity Index (DTI) to assess the risk of screw cut-out. A retrospective analysis of 306 proximal humerus fractures treated with PHILOS Plate.

doi:10.21203/rs.3.rs-1650855/v1

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Applying the Deltoid Tuberosity Index (DTI) to assess the risk of screw cut-out. A retrospective analysis of 306 proximal humerus fractures treated with PHILOS Plate.

https://doi.org/10.21203/rs.3.rs-1650855/v1

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Background. Reconstruction of the proximal humerus with a locking plate is often the first approach for proximal humerus fractures. Screw cut-out is the most common complication and is especially relevant in osteoporotic bone of the elderly population. The Deltoid Tuberosity Index (DTI) has recently been proposed as an indirect measure to assess osteopenia and failure rate before surgery, which may provide important information for surgical planning. Though simple and assessable, the DTI lacks scientific evidence to back its broad clinical usage. This study gives the first independent, large-sample retrospective analysis of the correlation between the local bone density, indirectly measured through the DTI, and screw cut-out.

Methods. 306 cases of proximal humerus fractures treated with PHILOS plate were retrospectively analyzed. The DTI was measured in AP x-rays. The primary endpoint was screw cut-out defined as the intra-articular position of at least one screw associated to a reduction loss after surgery.

Results. The mean clinical follow up was 467 days. The DTI varied from 1.10 to 2.28 (average: 1.42). Screw cut-out occurred on average in 8% of the cases and did correlate positively with a DTI ≤ 1.44 (p = 0.003). However, the rate of cut-out and correlation to DTI varied widely according to age group: within the age of 65-80 years a DTI ≤ 1.44 increased the cut-out rate from 0% to 17% (p = 0.02); on the other hand, in younger ages (< 65 years) the DTI did not correlate to cut-out and in the oldest group (> 80 years) cut-out rates were high (17-20%) independently of the DTI. Age and medial hinge displacement also correlated to cut-out. This was not the case for gender, fracture pattern and quality of surgical reduction.

Conclusions. We confirm the correlation between a DTI ≤ 1.44 and screw cut-out. This correlation alone however may be too simplistic and not relevant in all age spectrum. High risk groups for screw cut-out are patients older than 65 years with a DTI ≤ 1.44 or any patient older than 80 years. Applying the DTI in the age group of 65 to 80 years offers relevant information for surgical planning in the trauma setting through a tool that is fast, cheap, and easy to perform.

Level of Evidence: Level 3, Retrospective Cohort Study.

Proximal humerus fractures

Deltoid Tuberosity Index

DTI

osteopenia

failure of osteosynthesis

screw cut-out

Proximal humerus fractures are common and often treated with locking plates, such as the PHILOS Plate[1, 2]. The most common complication of this surgery is screw cut-out, reported in 8 to 57% of the cases[3, 4]. This complication often affects the quality of life due to its association to shoulder pain and restricted range of motion. Screw cut-out may be defined as the disruption of the humeral head by the cranial screws in the context of a reduction loss. Since older age and a low local bone mineral density (BMD) are known independent predictive factors for cut-out, a preoperative assessment of bone quality is often recommended to better predict the risk of surgery failure[5–8]. However, the standard methods of osteoporosis diagnosis (Dual-energy-x-ray and peripheral quantitative CT) are not routinely available in the trauma setting and could significantly delay treatment[4, 6, 9]. To indirectly assess bone mineralization, several parameters have been proposed. Tingart et al. proposed measuring the combined cortical thickness of the humeral diaphysis, while Newton et al. used the cortical thickness to calculate a medial cortical ratio[10, 11]. Though a correlation between cortical thickness and BMD has been confirmed, its adoption is limited since many x-rays from proximal humerus fractures do not include the middle diaphyseal area needed for Tingart’s and Newton’s measurements[12]. The Deltoid Tuberosity Index (DTI), proposed by Spross et al., has the advantage of measuring the cortical thickness on the proximal humerus (above the deltoid tuberosity) and demonstrated a strong correlation to local BMD[12]. The smaller the DTI value, the thinner the cortex and therefore the greater the correlation to osteopenia. A DTI cut-off of 1.44 predicted a low bone mineral density (< 80 mg/cm3) of the humeral head (sensitivity, 0.9; specificity, 0.8). The authors concluded in 2017, on a further retrospective study with 146 patients, that a DTI ≤ 1.44 was a relevant predictor of cut-out in proximal humerus fractures and claimed for further research[13]. Though this index seems to grow in popularity, there were yet no clinical studies supporting the use of this tool and a recent study with a small sample size of 48 geriatric patients found no correlation between osteopenia, measured by DTI, and surgical outcome[14].

This study aims to give an independent, large-sample retrospective analysis of the correlation between the local bone density, indirectly measured through the DTI, and the most common post-surgical complication after ORIF with locking plate osteosynthesis – screw cut-out.

We retrospectively collected data from all patients operated in our level I trauma center, between 2007 and 2018, which met the following inclusion criteria: isolated proximal humerus fracture, no previous shoulder surgery, preoperative electronic anteroposterior (AP) x-ray in internal rotation as well as outlet view, treated surgically with an internal locking plate (PHILOS Plate). Exclusion criteria included: pathological fracture and a follow-up of less than 6 weeks. No patients were treated with a fibular graft, supplemental plate, or other augmentation strategies.

The DTI was retrospectively measured in AP x-rays immediately above the upper end of the deltoid tuberosity where the outer cortical borders become parallel, as described by the proponents of the index[12]. The DTI value is given by the ratio between the external cortex and the internal endosteal diameter (Fig. 1). The data was collected by three of the authors, all experienced trauma surgeons. Measurements were performed through an electronic length-measuring tool provided by IMPAX^TM software, regularly used in our hospital. Fractures were classified according to AO/OTA classification and Neer classification. Metaphyseal head extension and medial hinge displacement were measured according to Hertel et al.[15].

The rehabilitation protocol included free active range of motion exercises since day one after surgery and no lifting or pulling tensions of the injured arm for 6 weeks. Follow-up x-rays were performed after 6 weeks and strengthening exercises were then initiated. Further follow-ups were only performed in case of existing symptoms. The number of screws and grade of reduction were assessed in the postoperative x-rays (AP and outlet view) taken usually on the second day after surgery. Reduction was categorized as anatomic (< 2 mm of displacement), acceptable (< 1 cm or < 45° of displacement of any fragment) or dislocated (none of the previous).

The primary endpoint was screw cut-out defined as the intra-articular position of at least one screw, associated to a reduction loss after surgery. Intra-articular screws identified within the first days after surgery without reduction loss were considered as iatrogenic malposition. Intra-articular screws without reduction loss and associated to a progressive bone mass reduction and deformity of the humeral head were classified as humeral head necrosis.

Statistical Analysis

Statistical analysis was performed using JASP (0.11.1 / October 7, 2019 – jasp.stats.org) provided by the University of Amsterdam (Amsterdam, The Netherlands). Descriptive statistics included means, standard deviations, ranges and proportions. Inferential statistics included the t test for numerical data and χ2 test for categorical data. Exploratory data analysis was performed using multiple logistic regression. The significance level was set at a p value = 0.04.

A total of 306 patients met the inclusion criteria. The mean age was 61.5 and 60% were female. The mean follow up was 467 days (min: 42 - max: 4742).

Deltoid Tuberosity Index

The DTI varied widely, from 1.10 to 2.28 (average: 1.42). A total of 173 patients (57%) had a DTI smaller or equal to the predefined cut-off value of 1.44, which included patients from a wide age spectrum (27–94 years). The average age of this group was 67 and 64% were female. Factors that significantly correlated (p < 0.001) to a smaller DTI were an older age, female gender, higher ASA score, lower height, lower weight and therefore a lower BMI. Knowing the established correlation between DTI and bone mineral density, this correlation presented as expected. There was no correlation between DTI and fracture pattern. Patients with a DTI ≤ 1.44 stayed in the hospital on average 2 days longer after surgery (p = 0.015) and had a significantly higher risk of screw cut-out (12 % vs. 2%, p = 0.001). No correlation was found between DTI and other postoperative complications (Table 1) and, in particular, there was no significant difference in the conversion to shoulder prosthesis (average of 4%). DTI also did not correlate to conversion to prosthesis within different age groups: in the younger population (< 65 years) the conversion rate was 2%, 6% for the 65–80 years group and 8% for the older group (> 80 years).

Table 1

Correlation between screw cut-out and postoperative complications/data.
AFTER SURGERY & COMPLICATIONS	Total (306)	DTI ≤ 1.44		P-Value
AFTER SURGERY & COMPLICATIONS	Total (306)	No (133)	Yes (173)	P-Value
Time from Surgery to Discharge (d)		4	6	0.015
Iatrogenic Malposition	2%	2%	2%	0.870
Implant Removal	32%	34%	31%	0.627
Total Complications	36%	29%	42%	0.018
Infection	4%	3%	5%	0.470
Non-Union	6%	7%	6%	0.733
Cut-out	8%	2%	12%	0.001
Time Surgery to Cut-out (d)	55	55	62	0.781
Humeral Head Necrosis	4%	4%	4%	0.890
Plate/Screws Break	1%	2%	1%	0.418
Motor Deficit / Impingement	9%	7%	10%	0.260
Iatrogenic Nerve Lesion	1%	2%	1%	0.202
Omarthrosis / Pain	6%	6%	5%	0.768
Conversion to Prosthesis	4%	4%	5%	0.710
within < 65 years	2%	1%	4%	0.749
within 65–85 years	6%	11%	4%	0.211
within > 85 years	8%	17%	7%	0.418

Screw cut-out

Screw cut-out occurred in 24 cases (8%) and was diagnosed on average 55 days (min: 24; max: 726) days after surgery. A summary of preoperative risk factors for cut-out can be found in the Table 2. A relevant correlation was found for age, DTI, medial hinge displacement and ASA 4. No cut-out occurred with a DTI > 1.53 (Graphic 1). Gender and fracture pattern did not correlate to cut-out.

Table 2

Preoperative risk factors and its correlation to screw cut-out.
	Total (306)	Cut-out		P-Value
	Total (306)	No (282)	Yes (24)	P-Value
Age (y)	61.5	60	73.5	< 0.001
Gender (F)	60%	59%	67%	0.475
BMI	25.7	25.7	26	0.532
AO Fracture Type
A	24%	24%	21%	0.690
B	57%	57%	54%	0.755
C	19%	18%	25%	0.404
Neer Fracture Type
2	27%	28%	21%	0.449
3	36%	37%	29%	0.326
4	36%	35%	50%	0.135
DTI	1.42	1.43	1.35	0.003
Medial Hinge Displacement	78%	77%	96%	0.031
Initial Neck-Shaft-Angle (°)	149	149	143	0.536
Valgus (> 140°)	60%	61%	54%	0.534
Normal (120–140°)	24%	24%	29%	0.558
Varus (< 120°)	14%	14%	17%	0.739
Metaphyseal Head Extension (mm)	11.8	11.3	12.9	0.906
ASA Score
1	18%	19%	8%	0.201
2	56%	57%	54%	0.812
3	24%	25%	33%	0.342
4	0%	0%	4%	< 0.001
Days until Surgery	1	1	1.5	0.527

Since age played a relevant role in the occurrence of cut-out, a correlation test between DTI and screw cut-out was performed for three different age groups (< 65, 65–80 and > 80 years). Between the ages of 65–80, a smaller DTI did significantly correlate with a higher rate of screw cut-out (17% vs 0%, p = 0.02). No correlation was found in the younger and older groups. From the total of 306 patients, a high-risk group with a cut-out rate higher than 17% was identified. This included all patients older than 80 years independently of DTI, or older than 65 years with a DTI ≤ 1.44 (Table 3). No correlation was found between cut-out and surgical data such as quality of reduction, final neck-shaft angle, time until discharge and wound infection rate (Table 4). The strategy chosen after the diagnosis of screw cut-out was adapted to the severity of the cut-out, resulting symptoms, age and expectations/preferences of the patients. While in 38% physiotherapy alone was the therapy of choice, in the remaining 62% surgery was needed (Table 5).

Table 3

Rate of screw cut-out within age groups and correlation to DTI.
	Cut-out
Age	DTI ≤ 1.44	DTI > 1.44	p
< 65 years (173)	0%	5%	0.053
65–80 years (97)	17%	0%	0.022
> 80 years (36)	20%	17%	0.851

Table 4

Correlation between screw cut-out and operative and postoperative data.
SURGERY & COMPLICATIONS	Total (306)	Cut-out		P-Value
SURGERY & COMPLICATIONS	Total (306)	No (282)	Yes (24)	P-Value
Reduction
Perfect	26%	27%	13%	0.113
Acceptable	48%	48%	50%	0.867
Dislocated	25%	24%	38%	0.160
Final Neck-Shaft Angle (°)	133	133	131	0.118
Varus (< 120°)	10%	9%	17%	0.239
Valgus (> 140°)	23%	23%	25%	0.828
Days from Surgery until Discharge	5	5	6	0.062
Infection	4%	4%	4%	0.949

Table 5

Therapy of choice after screw cut-out diagnosis.
AFTER Cut-out	Total (24)
Physiotherapy without Surgery	38%
Implant Removal	33%
Re-Osteosynthesis (PHILOS)	13%
Shoulder Prosthesis	27%

Within our sample of 306 patients, the DTI was easy to measure and did present a positive correlation to older age, female gender, higher ASA score and lower BMI. This was to be expected considering its correlation to BMD described by the proponents of the index and confirmed in following independent studies[12, 14, 16]. Interestingly, a lower DTI did not correlate to fracture pattern, which remains a controversial subject with some authors confirming[17, 18] and some denying this correlation[14].

The average general complication rate was 36%, being screw cut-out the most common complication (8%). Though screw cut-out did correlate positively with a DTI ≤ 1.44 (p = 0.003), this correlation varied widely between age groups. While within the ages of 65–80 a DTI ≤ 1.44 raised the cut-out rate from 0–17% (p = 0.02), in younger ages (< 65 years) the DTI did not correlate to cut-out. In the oldest group (> 80 years) cut-out rates were high, independently of the DTI (17% vs 20%) (Fig. 2). Besides the first publication of Spross et al. on the correlation between DTI and cut-out (with 146 patients), this hypothesis has only been tested once, by Taskesen et al. (with 48 geriatric patients, 50–95 years old), in a study that failed to confirm the correlation of DTI to surgical failure[14].

More than merely an academic value, the DTI has the potential to improve treatment in the trauma setting. As reported here, patients between 65 and 80 years old with a DTI ≤ 1.44 have a significantly higher risk of developing screw cut-out and should therefore be treated with the precautions typical of the elderly (> 80 years) population (Fig. 3). Recently recommended strategies for patients with high risk for failure of osteosynthesis due to osteoporosis include: restoring the medial column (if needed with addition of a fibular graft or an anterior plate), reverse drilling within the humeral head to avoid disruption of the articular surface, fixation with at least 5 head screws and at least one calcar screw, cement augmentation of the head screws, and careful assessment of the patients that should instead be treated primarily with a prosthetic approach[4].

Previous studies stated the relevance of an insufficient medial support (no cortical or screw support) for screw cut-out[7, 13]. We confirm the correlation between medial hinge displacement (MHD) before surgery and cut-out. In 96% of all cut-out cases there was an underlying MHD. Though the correlation between both 3-part and 4-part fractures as well as an inadequate reduction are often reported to correlate to surgery failure, our data failed to support such statements[6].

In 62% of the cases of screw cut-out a second surgery was needed, and in 27% of the cut-out cases a conversion to shoulder prosthesis was performed. Though the DTI did show a correlation to cut-out, no correlation to its therapeutic consequence could be found. While in the group with a DTI ≤ 1.44 a conversion to shoulder prosthesis happened in 5% of the cases, in the rest of the population this percentage was 4% (p-value not relevant). The rate of conversion to prosthesis also did not correlate to DTI within age groups.

Limitations, considerations and strengths of this study

Screw cut-out was diagnosed on average 55 days after surgery. Our follow-up protocol recommended x-rays after 6 weeks, which imposes a bias over the diagnosis timing. It cannot be ruled out that the actual time of cut-out may occur earlier. Similarly, asymptomatic cut-out (described as high as 7%) or cut-out in elderly patients with limited mobility may remain undiagnosed[19]. Finally, an alternative x-ray combination of AP in external rotation plus axial view in 30° (not standard in our hospital) has been reported to have a higher sensitivity for detecting screw cut-out[20]. For these reasons, it is plausible that the actual cut-out rate may be higher than the 8% we observed.

The major strength of this study is to provide the first large-sample independent study on the DTI and its correlation to screw cut-out after it was first reported by its proponents in 2017. Furthermore, the combination of age groups and DTI clarifies and increases the utility of this index in the trauma setting.

The Deltoid Tuberosity Index (DTI) is a simple method to indirectly assess local bone quality. We confirmed the correlation between a low DTI and screw cut-out. This correlation alone however may be too simplistic and should be assessed together with patients´ age. High risk patients for screw cut-out are those older than 65 with a DTI ≤ 1.44 or any patient older than 80 years old independently of the DTI. In these cases, the observed cut-out rate surpassed 17%. Applying the DTI in the age group of 65 to 80 years offers relevant information for surgical planning in the trauma setting through a tool that is fast, cheap and easy to perform. Furthermore, this method does not require any additional exposure of the patient to radiation as it utilizes the standard performed x-rays. Above the age of 80 years the risk of cut-out is high independent of cortical thickness.

AO/OTA - AO Foundation/Orthopaedic Trauma Association

ASA - American Society of Anesthesiology

BMD - Bone Mineral Density

DTI - Deltoid Tuberosity Index

MHD - Medial Hinge Displacement

Ethical Approval:

This is an observational study. The Ethics Committee of the University of Tübingen has confirmed that no ethical approval is required.

Consent to Participate:

Do not apply.

Consent to Publish:

Do not apply.

Availability of data and materials:

The data presented in this study was retrospectively collected between 2008 and 2018, from the electronic files of the patients treated at our department (Department of Orthopaedics and Trauma Surgery, Klinikum Stuttgart). This data is available for independent inspection or reevaluation at any time, given explicit permission of the Head of the Department.

Competing Interests:

None. There are no financial or non-financial interests directly or indirectly related to the work submitted for publication.

Funding:

Nothing to declare.

Author contributions:

All authors contributed to the study conception and design. Material preparation and data collection were performed by Tomas Da Silva, David-Benjamin Ehrhard, Theo Manuel Chuchuy and Tobias Merkle. Statistical analysis was performed by Tomas Da Silva. The first draft of the manuscript was written by Tomas Da Silva and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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No competing interests reported.

Graphics1.png
Graphic 1. DTI dispersion within the groups with and without screw cut-out. Average DTI for patients with cut-out was 1.35 (min:1.16, max:1.54) and for patients without cut-out 1.43 (min:1.10, max:2.28).

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Applying the Deltoid Tuberosity Index (DTI) to assess the risk of screw cut-out. A retrospective analysis of 306 proximal humerus fractures treated with PHILOS Plate.

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Abstract

Figures

Introduction

Methods

Statistical Analysis

Results

Deltoid Tuberosity Index

Screw cut-out

Discussion

Limitations, considerations and strengths of this study

Conclusion

ABREVIATIONS

Declarations

References

Additional Declarations

Supplementary Files

Status:

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