European Journal of Cardiovascular Medicine

Ulna is the medial bone of forearm which plays significant role in formation of proximally elbow joint, distally wrist joint. Ulna is not a perfectly straight bone. It is curved in both anteroposterior and mediolateral planes. Throughout its whole length, it forms a gentle curve whose convexity is directed backwards. In addition, the upper half shows a curvature to the lateral side and the lower half or less shows a similar curvature to the opposite side. This backward bending is lost in plastic deformation and presents as positive ulnar bow sign.¹

In children bowing of long bones is common due to increased plasticity. The term ‘‘ulnar bow sign’’ was first described by Lincoln and Mubarak in 1994.¹ Line along the posterior border of the ulna on a true lateral radiograph should be a straight line and any deviation should lead to suspicion of ulnar bowing and associated pathologies significant.^1,2,3

Bowing in forearm is common because trauma to the forearm are common in children and also both the radius and ulna are of comparable diameter and are naturally curved bones so small magnitude longitudinal forces can cause bowing and some magnitude of transverse forces can also cause bowing in these bones⁴ .The ability to bend or bow in children occurs because the cortex is thinner in absolute and relative terms to the adult bone and because of the way the cortex and periosteum bind to each other in a developing skeleton ,a force greater than mechanical strength /tenacity of the bone leads to bowing_. ^5,6 The plastic deformity in ulna which has more than 10 degrees of angulation /bowing deformity do not remodel back on its own and need closed/open /surgical intervention especially in children above 10 years of age⁷_. Present study was aimed to assess maximum ulnar bow and apex ratio in normal children 2-12 years of age at a tertiary care teaching hospital.

The present study was a prospective, descriptive study, conducted in the Department of Orthopaedics Dr. Rajendra Prasad Government Medical College, Kangra, Tanda, Himachal Pradesh, India. Study duration was of 2 years (July 2018 to June 2019). Study was approved by institutional ethical committee.

Inclusion criteria

• All patients with forearm injuries with normal contralateral forearm/normal bilateral forearm 2-12 years of age presenting to the Department of Orthopaedics, parents willing to participate

• Exclusion criteria
• Children less than 2 years OR more than 12 years
• Preexisting trauma
• Tumours of forearm
• Deformities
• Neurological disorders.
• Patients not giving consent for participation in the study
• Injury bilateral forearm
• Patients with congenital deformities around the forearm bilaterally

The Performa included the details on name. age, sex, side and CR. amount of MUB, Apex Ratio of the patient on an excel data sheet. The subjects were sent to radiological examination using X rays as investigation modality. The X-rays were previewed and lines were drawn independent of radiologist on the radiographs as per the criteria already mentioned and will be reviewed with radiologists.

True lateral views of forearm were done. Forearm radiographs were obtained using our routine protocol. Briefly, the child was placed in a seated position (younger children allowed to sit on a carer’s knee). The arm was carefully raised and placed on a table with the height adjusted such that the shoulder, elbow, and wrist lay on the same horizontal plane. The elbow was flexed to 90 degrees, and the medial aspect of the arm was rested directly on the cassette. The hand and wrist were externally rotated until both styloid processes superimposed. This position was maintained by resting a sandbag against the palm or by the hand of the carer.

The assessment of ulnar bow was performed by using standard true lateral x ray film and scale. A straight line was drawn along the dorsal border of the ulna from the level of the olecranon to the distal ulnar metaphysis, which was referred to as the ulnar straight line. The maximum perpendicular distance of this line from the ulnar shaft, maximum ulnar bow (MUB), was measured by using scale.

We measured the full-length of the ulna from olecranon tip to ulnar distal metaphysis tip on dorsal aspect by using scale. The Apex ratio is the distance from distal Ulnar metaphysis to the MUB point divided by total length of ulna from distal ulnar metaphysis to olecranon tip x100. KIM ELBOW SCORE was calculated in patients with ulnar bow by looking for any visible deformity, asking for any pain during movement, by calculating range of motion that is flexion plus extension and pronation plus supination and asking questionnaire for function giving a maximum score of 5 for each questionnaire.

The data was entered and cleaned using Microsoft excel spreadsheet. The data was analyzed using (Statistical Package for Social Sciences) SPSS version 22. The quantitative data was checked for normality using the Kolmogorov-Smirnov test. The quantitative data was expressed in means and standard deviation. The comparison of the quantitative variables was compared between the two studies using unpaired t-test. A p-value of less than 0.05 was considered to be statistically significant.

There were 122 children who were enrolled in our study. The mean age of the children was 7.11 ± 1.92 years. The age of the children ranged from 3 to 12 years. Majority children were from age group of 7 to 8 years (37.7 %) followed by age group of 5 to 6 years (27.9 %). There were 63 boys and 59 girls. The boy to girl ratio was 1.06:1. 48 children had a history of fall, 72 children had no history of trauma, and 2 children had a history of road side accident.

Table 1: General characteristics of children

There were 122 limbs which had undergone X ray of forearms. X-ray was done for 54 left and 68 right forearms.

Table 2: Limbs x-rayed

The ulnar bowing was assessed through Maximum Ulnar Bow (MUB) which was calculated as the maximum perpendicular distance between a straight line (drawn along the dorsal border of the ulna from the level of olecranon to the distal ulnar metaphysis) and ulnar shaft. The MUB was present in 10 children. The mean MUB was 0.20 (SD=0.05) cm. The MUB ranged from 0.12 cm to 0.29 cm.

We also calculated the apex ratio as the distance from the apex to the tip of the total length of Ulna. So, the mean total length of ulna (Measurement A) in our study was 17.04 (SD=2.38) cm, ranging from 13.14 cm to 19.75 cm. Also, the mean distance from the apex to the tip (Measurement B) was found to be 3.69 (SD=2.01) cm, ranging from 1.43 cm to 7.70 cm. The mean apex ratio was found to be 0.21 (SD=0.10). The range of apex ratio was between 0.10 and 0.44.

Table 3: Maximum Ulnar Bow and Apex Ratio of children

6 boys & 4 girls showed bowing in their ulna. The mean MUB in was more in boys (2.1±0.57 mm) as compared to that in girls (2±0.6 mm) in girls. But this was statistically comparable p=0.86.

Table 4: MUB comparison in Boys and Girls

Figure 1: MUB comparison in boys and girls

Kim elbow scores were found to be full in case of all 10 children with ulnar bow, there was no gross deformity which could hinder in day-to-day activities in all these children. There was no pain on normal movement at the elbow and wrist, there was no loss of normal range of motion at the elbow and patient had no difficulty in doing daily activities like combing hair, feed oneself, open door knob, hold overhead and putting in shoes.

Table 5: Kim elbow scores in children with ulnar bow

Very little literature is available on the ulnar bow and apex ratio in paediatric population in the world and almost no data is available on normal physiological bow in ulnar bone in developing countries. Values obtained from western literature can’t be applied blindly on our population. In present study, 122 cases (63 boys and 59 girls) were enrolled, with mean age of 7.1 years with 50 children presented with trauma to opposite limb /lower limbs and other 72 had no history of trauma.

Table 6: Present study showing patients with MUB and Apex Ratio

The maximum ulnar bow was found in 10 children out of 122 enrolled with range of 1.2mm-2.9mm (mean 2.0 mm) and Apex Ratio of 10%-44% (mean 21%) The studies conducted till date pertaining to ulnar bow were conducted in traumatic limb to diagnose the missed radial head dislocation in patients with no obvious ulna fracture .The patients were mostly paediatric population up to 13-14 years of age and the Monteggia fractures and its variants were missed on the initial presentation of patient as Ulnar Bow was not calculated leading to missed Monteggia fractures .Misdiagnosis led to added morbidity and an increased risk that an open surgical procedure will be necessary to achieve reduction of the dislocated radial head ,so here lies the importance of our study to know how much bow can be labelled as normal physiological Ulnar bow_.¹

In Lincoln and Mubarak Study,¹ the maximum ulnar bow in patients with radial head dislocation without fracture of the ulna Measured an average of 3.9±0. 4 mm. This maximum ulnar bow in the control group of Uninjured extremity revealed a bow of 0.01±0.1mm. The ulnar bow in our study came out be on an average of 2±0.03mm. In Shigaku Sai et al.,⁷ study the average age of children enrolled was 8.4 years.

In this study maximum ulnar bow was 7.5 mm with an average bow of 5.9mm. In Sakae Sano et al.,³ study MUB was 4.4 mm (range 3-7 mm and the average apex ratio was 49.2% (range 47-52%). In Vivek Singh et al.,² study the maximum ulnar bow had a range (from 2.3 -6.5 mm) an average MUB of 4.7mm.

In the above studies traumatic bow was found to be more (>4) and significant from our study and the bow was located at almost 50 percent of the length of the ulna but in our study the mean apex ratio percent was around 20 percent of length that is more distal to the whole ulnar length in comparison to traumatic studies.

Table 7: Comparison of Studies in reference to MUB

In all traumatic studies ulnar bow was statistically significant from our study as p value is less than <0.05 which signifies that bow present in our study can be a normal physiological bow. In all the cases in our study true lateral radiographs were obtained keeping in view the Skibo and Reed criteria^10. 10 cases with positive ulnar bow in our study were thoroughly examined for any radiocapitellar line disruption to rule out any incongruity between capitellum and the radius, it was found out to be normal alignment in all cases^20.

All cases with Ulnar Bow in our study were examined for Kim Elbow Scores and all children had a full score of Elbow function while in other traumatic studies there was restriction of pronation, supination, flexion and extension during presentation³. Our study participants had full Kim Elbow score of 100 in comparison to traumatic studies in which Elbow Score was on an average <90.

This is the first of its kind of study as no other mass study is available in the world on atraumatic normal ulnar bowing However the sample size taken for the study can’t be applied to the whole population as whole, so many more multicentric studies with a larger sample size are required in the near future so that this could be standardized. Better methods like Computer Aided System can be used for the measurement and detection of Ulnar Bow in further research.

It is concluded from our study that Atraumatic Ulnar Bow found in our population was far less in magnitude than the ulnar bow found in the traumatic case reports and studies done in western population and elbow range of motion in our study was found to be normal according to Kim Elbow Scores. So, the bow found out can be a normal bow as there is no history of the trauma to the limb examined and no limitation of function and well could be due to normal physiological remodeling in the paediatric population. Ulnar Bow greater than 2 mm could raise suspicion of microfractures and need for CT evaluation for stress fractures.

Conflict of Interest: None to declare

Source of funding: Nil

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